PEER REVIEW HISTORY ARTICLE DETAILS TITLE (PROVISIONAL)

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1 PEER REVIEW HISTORY BMJ Open publishes all reviews undertaken for accepted manuscripts. Reviewers are asked to complete a checklist review form (see an example) and are provided with free text boxes to elaborate on their assessment. These free text comments are reproduced below. Some articles will have been accepted based in part or entirely on reviews undertaken for other BMJ Group journals. These will be reproduced where possible. TITLE (PROVISIONAL) AUTHORS REVIEWER REVIEW RETURNED THE STUDY RESULTS & CONCLUSIONS GENERAL COMMENTS ARTICLE DETAILS HEALTH CARE CONSULTATION AND SICK LEAVE BEFORE AND AFTER NECK INJURY: A COHORT STUDY WITH MATCHED POPULATION-BASED REFERENCES Englund, Martin; Jöud, Anna; Stjerna, Johanna; Malmström, Eva- Maj; Westergren, Hans; Petersson, Ingemar VERSION 1 - REVIEW Lena Holm, IMM, Division of Epidemiology Karolinska Institutet. Stockholm I declare I have no competing interests in this manuscript 22-May-2013 Item nr 3 and 6 needs to be clarified more, see attached review document. The statistical methods also need further calrfication and possible also some changes. Is the message clear? Overstaded, but could easliy be corrected OVERALL A well design study and well written manuscript with interesting findings and new knowledge. However, I have some key suggestions and comments. KEY MESSAGE The third bullet point is not well supported by the aim or the results of the study. How could consultation history be important to consider in tailoring treatment and rehab? I.e. what should be done differently in patients with previous health care consolations compare to patients without previous health care consultations? Further, health care consultations is a marker for ill-health, thus a thorough medical history is probably more relevant than the consultation history ABSTRACT Participants: The inclusion criteria; age (18 years or older) could preferable be included in the abstract. Results: Last sentence; Add information about if it is pre-, post- or all sick leave Conclusions The last part of the conclusions is not well supported

2 by the aim or the results of the study. How could consultation history be important to consider in tailoring treatment and rehab? I.e. what should be done differently in patients with previous health care consolations compare to patients without previous health care consultations? Further, health care consultations is a marker for illhealth, thus a thorough medical history is probably more relevant than the consultation history Instead, the conclusions about sick leave should be stated, since it was one of the aims of the study INTRODUCTION Pp5; Line 7. Ref 1 is s partly supporting the sentence, but the sentence should preferable be re-written, since approx. 50% of WAD occurred in impact directions other than rear-end. Pp 5 Line 27: Reference 15 does not support the sentence about the prevalence of psychological problems following whiplash trauma. Pp5 Line 42. Trauma related factors may better be replaced with post- collision health factors since it is not always obvious that the conditions are related to the trauma. The two references (2 and 3) are not optima. Ref 2 concerns acute WAD whereas Ref 3, refers to animal models and hypothesis. If re 3 is used, the sentence should point this out. Pp 5. Line 51: Neck pain intensity, cervical range of motion etc. are not necessarily trauma related. And the studies refereed to have not always measured these factors directly after the trauma, but rather with in the first few days or weeks after the collision. Pp6: Line 16: the objectives of the study.. before and after diagnosis of distortion of the cervical spine MATERIAL AND METHODS Pp 6. Line 53. Please specify which version of ICD.10 that was used for the periods. The ICD codes T91.8 A and T91.9. Sequelae of injuries (also called late whiplash) are not mentioned. 1) These should be included in the exclusion criteria for identification of both cases and references. They should also be included in the definition of the outcome (postcollision) with respect to health care consultations. Pp8: line 23/24. You write that you match the reference subjects based on among others study period It is unclear what you mean Pp 9. Outcomes, The categorization into low-frequent, frequent and high frequent consultation is not optimal. First, it is the labeling (wording). It may be better if they are with the actual categorization instead (0-1 etc) If you cannot analyze the number of consultations as a continuous

3 variable, which would be the optimal way, at least a crude sensitivity analysis should be reported, where you test various cut-offs. It would also be more informative if the cut-offs are based on consensus instead of a statistical cut-off. ( eg. 0-1, 2-4 per year more than 4.. The main problem with the current categorization is that the middle category covers 2-8 consultations, and constitutes a heterogeneous group with respect to consultations. Pp10: Sick leave: A more appropriate legend would be work disability. Furthermore, there is a need for a brief explanation of the difference between sick leave and disability pension in the Swedish Social Insurance system (according to the regulations at the time of your study). Figure 6 only covers 2 years before and 2 years after the time of diagnose. This is not explained in the methods and why not 3 years? RESULTS Make sure that you write the p in p-value either with uppercase letter as in the abstract OR lowercase letter (preferable) as in the Results Section, not both Pp 11. Line 39. How is acute visit in primary care ascertained and defined? Is it acute or is it sub-acute? Have you any information about day of collusion? If not, it may be difficult to determine whether it is an acute visit or not? Pp 12 Line It value that you have compared the low-frequent user and their transition into high-frequent user. However collapsing low-frequent and frequent consulters in the following results is a less good. These results are partly dependent on (influenced by) the first since low-frequent users constitute more than third of the collapsed group. I suggest that you isolate the frequent group, compare It to high-frequent users and present these results instead of the results from the collapsed groups. Pp 15. Table 3. Preferable add information about the variance within groups. Can you comment on the results of the high-frequent group, with respect to the mean increase in number of consultations especially concerning psychological distress? ( you do so in the discussion but may well be reported in the Result Section) Pp 16 line 5. Replace the legend Sick leave, with Work disability Pp 16 line 7. This is not a case cohort study.it is better to phrase the first sentence.., 96 subjects of the cases (6.7%) were on.. DISCUSSION PP18 Line: 15 I suggest a rephrasing of the sentence starting with Noteworthy,..in average about 16% developed a highfrequent consultation pattern that may be attributed to the injury. ( The results do not support your statement that this 16% persisted over at least 3 years You have calculated the mean over time (after injury but the curves in figure 5 shows a decrease after year 1

4 REVIEWER REVIEW RETURNED THE STUDY after the diagnosis.) Pp18. Line 17. You state: However in a sub group of patients, high level of health care consultations were noted already long before the neck injury diagnosis. This implies that a individually tailored multimodal rehabilitation is and important tool in the care and recovery process of a subset of patients after neck injury None of the references cited (17, 22) really support this. On the contrary, if any, there are some evidence that multidisciplinary rehabilitation do not have an effect on recovery following WAD. Cassidy, J. D., L. J. Carroll, et al. (2007). "Does Multidisciplinary Rehabilitation Benefit Whiplash Recovery?: Results of a Population-Based Incidence Cohort Study." Spine. Now, the study by Cassidy et al, did not specifically investigate the sub group of patients with massive health care consumption prior to an injury. Pp 19 Line: In reference 23,ONE possible reason for depression as a risk factor for WAD, may be an increased risk of collision due to the pre-collision mental conditions (poor concentration). However in the next sentence in that paper, the authors state that poor concentration is not likely to play a role in rear-end collisions. The way reference 23 is cited in your study is not completely correct. FIGURES Figure 5: Should be labeled months ( not month).. There is no explanation why you started 3 months prior to the diagnosis of neck injury and not 36 months as stated in the Method section Jordan Miller, School of Rehabilitation Science, McMaster University, Hamilton, Ontario, Canada 15-Jun-2013 Overall the study was well written, however, the manuscript would be strengthened by converting the use of the term 'neck injured individuals' to 'people with a neck injury' in order to use 'people first language'. Page 1, Line 6: The word still is not necessary. Page 1, Line 8: Tearing of should be replaced with injury to. There are many types of forces present in a whiplash injury, tearing implies shear and traction force, but I there are more possible explanations than tissue tearing. Page 1 Line 15: pain sensitization needs definition. Perhaps this would be better stated as sensory hypersensitivity and if this statement is made, I think elaboration of tis prognostic indicator is needed (ex: pain pressure, cold hyperalgesia, locally vs. distally) L40-42: You describe prognostic indicators present before trauma and prognostic indicators at the time of trauma, but are there also post trauma prognostic indicators?

5 REVIEWER REVIEW RETURNED THE STUDY RESULTS & CONCLUSIONS GENERAL COMMENTS Page 10, Line 50: Typographical error: 'rang sum' In the discussion, the classification of the neck injury using S13 was discussed as a potential limitation. I think this is an important part of the discussion that should be elaborated upon. i) In the introduction, the reader is led to think that people who's diagnosis is provided as S13 are primarily whiplash injuries. Is there evidence suggesting this is how whiplash injuries are coded? ii) Is 'sprain or strain' of the neck the most appropriate description of a traumatic neck injury. iii) In the ICD-10 CA WAD 1-3 are classified as S1340-S1342. Were these classifications not available for the physicians who are making the diagnosis? iv) Why was the analysis performed on S13 and S16, S130, S142, etc. were not included? This is not meant to criticize the decision to use only this classification, but I think it is important that the reader understand the rationale for the decision. Also, if S13 is being used to try to target traumatic neck injuries with a whiplash mechanism, sufficient evidence is needed to suggest that S13 is made up of primarily whiplash injuries. Otherwise, this may need to be reframed to suggest the population represents 'people who were diagnosed by their physician as having a sprain or strain of the neck. Daniel Pinto Assistant Professor, Department of Physical Therapy and Human Movement Sciences/Center for Healthcare Studies, Feinberg School of Medicine, Northwestern University USA I have no competing interest 27-Jun-2013 Description of methods: There could be a more precise reporting of methods which would specific in greater detail which statistical tests were performed with a given variable. All of the statistical tests were reported but it would have been helpful to know whether in a given situation the researchers were comparing count data versus proportions. Also, it was unclear whether there was justification for use of t-tests with count data. This would require that a large number of levels were present in the data. the results section is lacking organization The conclusion that consultation history be taken into account when tailoring individual treatment seems premature considering there was no discussion about how this might happen. In fact, the study doesn't discuss optimal health care use at all which may fall somewhere between the low users and high users. They used four matched controls per case with sensitivity analyses based on matched variables. However, this paper makes for difficult reading on account of poor organization and a lack of clarity concerning methodology. Specific comments: Pages 2-3 Abstract:

6 Objectives: could introduce rationale from line 1 page 4 into objectives in abstract providing reader with context of study. Conclusions: It is not clear how consultation history should be taken into account. Unless authors propose some suggestions as to how this might be realized, I suggest this statement be altered. Page 4 Article summary: Strengths and limitations: Potential misclassification bias toward showing less difference between groups... This was not well discussed in the limitations section of the article. How do the authors suggest this might produce this bias? This requires further explanation in the discussion section to earn inclusion in the summary. Page 5, Introduction, top of the page, line 0 the sentence beginning with the so called whiplash... Are the authors specifically speaking of injuries to soft tissue structures? If so, for clarification it is suggested that the words soft tissue be inserted between several and structures in the sentence. Additionally, the word capsule following facet joint is suggested. Page 5, line 37. The sentence beginning with Recent studies have reported... is introducing the relationship with pre-injury consultation rate and post-injury utilization. This is further developed in the paragraph beginning on the top of page 6 and it is suggested that this sentence be moved to the beginning of the paragraph on page 6. Methods: It was confusing that sick leave was captured only for two years post injury and the rest three years post injury. In part, changing the location at which this information is presented in the methods section may alleviate this. Sick leave timeframe is located in the data sources subsection and the follow-up of the subjects was reported in the Neck injury cohort subsection of Study cohorts. It is suggested that the sentence sick leave data was available... on page 7 be moved to page 8 at the end of the Neck injury cohort subsection. Page 7 under neck injury cohort, the sentence starting with We excluded all cases... It may be clearer to write out the range in years as between 1998 and up until the month before diagnosis. Reference cohorts - Is there a reason why reference 3 was not the only cohort included in the study? For example, were there concerns with overmatching? It is suggested that Table 1 be moved to the results section as it includes a description of the cohorts based on educational level. Outcomes: Page 9. Why was two years before injury chosen as the timeframe to categorize patients as low, frequent, or high-frequent users? It seems odd that total information was captured for all participants three years before injury and all of the data was not used to categorize these patients. How might the story change if all of this

7 data was used. Statistical analysis This section could use more clarity in terms of identifying in detail which variables where analyzed with which statistical tools. Why not report Odds Ratios along with attributable risk? Multiple T-tests across subgroups are not typically suggested without error correction, it is suggested that the authors justify this practice. Also, please report that variance was equal across groups and a t-test taking unequal sample size into account was used. Also it appears that there was comparison of count data between groups, subgroups, and years using t-tests or non-parametric tests. This practice should be justified statistical analysis of count data as continuous is only acceptable if there are sufficient levels to each variable. Otherwise models could be constructed to take confounders into account and it is suggested that the authors consider analyzing the data using a Poisson distribution. Results: This section needs more organization. Please consider organizing according to Cohort characteristics Group results Stratified analyses Diagnoses treated Sick leave Changes over time (referred to in the analysis but not specifically addressed in its own section) Cohort characteristics: For clarity it is suggested that the words, in an acute, non-planned visit be added after the word physician in the first sentence in this section. Group results Consider reporting how the neck injured consulted as a group relative to the references in the 3 years prior to the injury. It is not surprising that they consulted more over the 6 year period when a major injury took place within this cohort. Top of page 12 first full sentence, starting with The mean age,... you speak to the neck injured and primary references here but in the next sentence you do not refer to any groups. Is the first sentence differentiated because the secondary references were different? If not, it is suggested that the words, neck injured and primary references of be removed from this sentence to improve clarity. Stratified analyses: (If I am understanding correctly the discussion of your stratified analyses starts on page 12, second paragraph) Page 12, second paragraph starting of the neck injured. It is suggested that this falls under a different heading as the outcome is not health care consultations per se, but the transition in healthcare user classification. This appears to be an area in which an odds ratio would be suitable. In the methods section outline for the reader that you intend to identify corresponding risk and attributable risk and how this is done. On page 9 you refer to assessing the absolute portion of those injured please describe how this was done for

8 your reader. Page 12, paragraph starting, In the stratified analyses,... see comments on Changes over time below. Please review your calculation of attributable risk. By plugging in the case-control numbers into an immediate form program in Stata, I obtained an Odds Ratio of 2.47 and attributable risk percentage of 59% for transitioning from a low/medium frequency user to a high frequency user following neck injury. In many respects this is expected in the first year of treatment. I would be interested in a table that reports the odds of transitioning from low frequency to high frequency at each year of follow-up. This nicely supports the introduction that there are a lot of people who are not improving following acute neck injury. Page 14, second sentence beginning with the proportion of subjects who were classified as low-frequent among neck injured... It appears prior to the injury there was a greater percentage of the neck injured group who were in the low-frequent consulters category 26 v 14% - is this a mistake? How does this fit into the overall message of the paper that the neck injured consulted more on average than the references? Also this sentence appears misplaced, it is suggested that this sentence would be better placed in page 12 within the paragraph starting, of the neck injured... Diagnoses treated The content on page 14 can be organized under this heading. Sick leave, Page 16 The sentence starting, Among the cases..., The mean number of sick days was higher but was this significantly different? Please clarify whether this difference was significant. The percentages reported in table 4 seem close for the low and frequent users. A correlation between sick leave days and health care consultations before injury is expected and not particularly newsworthy. In the final sentence, is the increase in sick days over the two years under study? How did year two look relative to year 1? Perhaps this could be considered in the next section my suggested reorganization is taken. Changes over time There is no specific discussion to changes over time in its own section but it holds so much importance to the message of this paper. It would be fitting to have a section specifically devoted to comparing baseline to Year 1 versus Year 2 versus Year 3. On page 12, the portion starting with, In the stratified analyses.... This would be great to move to this section and expand on it here. Discussion: Ultimately it is not surprising that individuals use more medical care following an acute neck injury (at 3-6 months) in fact, this may be an appropriate use of services. The fact that some low users of healthcare remain low users even after an acute injury may be problematic given the nature of the injuries under study. Might this, in fact, increase the likelihood that chronic pain becomes established? Do we know what they right use of healthcare services is? Perhaps this should be considered as a limitation or a discussion point. These subgroups may be poor representations of identifying what appropriate use might be.

9 However, it is interesting that individuals persist as high users of health care in subsequent years, up to year 3. I believe this article is best suited to focus on this in relation to appropriate use. If the conclusion states previous consultation history should be taken into account, how do the authors propose to do this? Via questionnaire at intake? How would management change? In the end you are saying that there are individuals who tend to use our health system differently low, frequent, and high users and this pattern changes slightly post injury. OK, how does this help me as a clinician? Table 3 is very busy and difficult to read. Table 4: I only compared the low-frequent groups on sick leave however, when comparing the proportions in table 4, although odds were increased for sick leave due to neck injury the 95% CI for the odds ratio crossed 0 and the chi square was not significant. By what methodology were significant differences found between these groups? I am assuming you tested the difference in the proportions here. This is where more specific detail is required in the methods section to allow a user to reproduce your results. Figure 4. In this figure it appears that there is also a transition from high to low utilization. This should be discussed as to why this might occur. Figure 5. Are we to assume that -3 months is representative of mean healthcare consultations over the previous 3 year period? Limitations: In addition to other suggested additions, please discuss the limitation associated with having to eliminate diagnoses from private care as noted on page 6 this will speak to the generalizability of these findings in countries where most of the management occurs in a private system. VERSION 1 AUTHOR RESPONSE Reviewer: Lena Holm, IMM, Division of Epidemiology Karolinska Institutet. Stockholm I delcare I have no competing interests in this manuscript OVERALL A well design study and well written manuscript with interesting findings and new knowledge. However, I have some key suggestions and comments. Authors' reply: We thank the expert reviewer for her positive response to our manuscript, and very much appreciate the thoughtful input provided. KEY MESSAGE The third bullet point is not well supported by the aim or the results of the study. How could consultation history be important to consider in tailoring treatment and rehab? I.e. what should be

10 done differently in patients with previous health care consolations compare to patients without previous health care consultations? Further, health care consultations is a marker for ill-health, thus a thorough medical history is probably more relevant than the consultation history Authors' reply: Thank you for highlighting this. We agree. Authors' action: We have deleted this implication throughout the manuscript. ABSTRACT Participants: The inclusion criteria; age (18 years or older) could preferable be included in the abstract. Authors' reply: We agree. Authors action: aged 18 has been inserted under the Participants subheading in the abstract. Results: Last sentence; Add information about if it is pre-, post- or all sick leave Authors' reply: We agree. Authors action: pre-injury has been added to the sentence. The sentence now reads: Number of days of sick leave pre-injury was associated with the number of both pre- and post-injury consultations (ρ= % CI , ρ= % CI ). Conclusions The last part of the conclusions is not well supported by the aim or the results of the study. How could consultation history be important to consider in tailoring treatment and rehab? I.e. what should be done differently in patients with previous health care consolations compare to patients without previous health care consultations? Further, health care consultations is a marker for illhealth, thus a thorough medical history is probably more relevant than the consultation history Instead, the conclusions about sick leave should be stated, since it was one of the aims of the study Authors reply: We have reconsidered that part of the conclusion. Authors action: The last paragraph now reads: Pre-injury levels of sick leave are associated with both pre-injury and post-injury levels of health care consultations. INTRODUCTION Pp5; Line 7. Ref 1 is s partly supporting the sentence, but the sentence should preferable be rewritten, since approx. 50% of WAD occurred in impact directions other than rear-end. Authors reply: We thank the reviewer for pointing this out. Authors action: We have in accordance with reviewer 2 deleted the word still in this sentence. Although, we have chosen to keep this reference on the rear-end collision as a common cause for neck injury, though we are aware of that other causes also are important. The sentence now reads line 3: One common cause for trauma resulting in pain and dysfunction of the neck is the rear-impact car crash.[1] Pp 5 Line 27: Reference 15 does not support the sentence about the prevalence of psychological problems following whiplash trauma. Authors reply: Thank you so much for mention this error, this article does not fit here. Author action: We have deleted this reference from the manuscript (line 12). Pp5 Line 42. Trauma related factors may better be replaced with post- collision health factors since it is not always obvious that the conditions are related to the trauma. The two references (2 and 3) are not optima. Ref 2 concerns acute WAD whereas Ref 3, refers to animal models and hypothesis. If re 3 is used, the sentence should point this out. Authors reply: We agree. Author action: We have deleted reference 3 (line 18) since this paper does not necessarily focus on technical aspects of the injury. We have changed trauma-related factors to post- collision health factors throughout the manuscript.

11 Pp 5. Line 51: Neck pain intensity, cervical range of motion etc. are not necessarily trauma related. And the studies refereed to have not always measured these factors directly after the trauma, but rather with in the first few days or weeks after the collision. Authors reply: We thank you for pointing this out. Authors action: We have made changes to clarify that these factors don t necessarily have to occur in a narrow time period around the collision. In line with your previous comment, we have changed terminology, from trauma-related factors to post- collision health factors throughout the manuscript. Pp6: Line 16: the objectives of the study.. before and after diagnosis of distortion of the cervical spine Authors reply: Thank you good suggestion on how to make our objective clearer. Authors action: Our objective in the introduction section has now been changed in accordance with that of the abstract. The sentence now reads (line 8): Hence, the objective was to study health care consultation and sick leave patterns before and after neck-injury (whiplash). MATERIAL AND METHODS Pp 6. Line 53. Please specify which version of ICD.10 that was used for the periods. The ICD codes T91.8 A and T91.9. Sequelae of injuries (also called late whiplash) are not mentioned. 1) These should be included in the exclusion criteria for identification of both cases and references. They should also be included in the definition of the outcome (post-collision) with respect to health care consultations. Authors reply: Thank you for highlighting these highly important aspects. The Swedish version of ICD10-SE, was used. Regarding late whiplash diagnosis; we chose not to exclude people with late whiplash diagnosis, given that they meet all inclusion criterions. However, only one (1) patients and nine (9) controls had a late whiplash diagnosis prior to inclusion, none of which was the primary cause for the consultation. In terms of the definition of outcome, late whiplash injury was included as all other causes for consultation, not specified. A total of diagnoses was registered for the cases in the post-injury period among these 294 (0.9%) was a late whiplash diagnosis T91.8/A and/or T91.9. Authors action: We have clarified the version of ICD-10 in the methods section page 6. Pp8: line 23/24. You write that you match the reference subjects based on among others study period It is unclear what you mean Authors reply: Thank you for noting this, this is a mistake (a left over from a previous version). Authors action: We have deleted this part of the sentence. The sentence now reads (line 7): To be able to compare the health care pattern and sick leave pattern of cases with the general population, we also assigned each case with four reference subjects randomly sampled from the Swedish population register matched for birth year, sex and area of residence (figure 1, table 1). Pp 9. Outcomes, The categorization into low-frequent, frequent and high frequent consultation is not optimal. First, it is the labeling (wording). It may be better if they are with the actual categorization instead (0-1 etc) If you cannot analyze the number of consultations as a continuous variable, which would be the optimal way, at least a crude sensitivity analysis should be reported, where you test various cut-offs. It would also be more informative if the cut-offs are based on consensus instead of a statistical cut-off. ( eg. 0-1, 2-4 per year more than 4.. The main problem with the current categorization is that the middle category covers 2-8 consultations, and constitutes a heterogeneous group with respect to consultations.

12 Authors reply: Thank you very much for these comments and suggestions on the cut-offs. We have thoroughly discussed the terminology within our group and other co-worker and also looked in published work to find the proper terminology to use. As there are no gold standard definitions, numerous ways of categorizations are possible and it s a trade-off not having too many subgroups compare to not having too large heterogenic groups. Still, categorization is often performed to simplify analysis and presentation; advantages that often outweigh the disadvantages. In the table below we give you the number of patients and references within each sub-group and the mean (median) number of consultations per year before and after injury for the patients (based on cut-offs as suggested by you) and old cut-offs used in manuscript. As can be seen although the actual figures differ a bit whit is expected the overall change within groups is similar. Pre-injury Post-injury New Old New Old Low-frequent (0-1) n=384 (vs. 384) 1.3 (1.8) 1.3 (1.8) 3.3 (6.3) 3.3 (6.3) Frequent (2-4) n=335 (vs. 583) 3.3(4.3) 4.7 (5.5) 6.0 (8.8) 6.7 (9.7) High-frequent (+4) n=724 (vs. 476) 11.0 (15.6) 15.3 (20.1) 11.7 (17.8) 15.0 (21.4) We politely suggest keeping the categorization as is. Pp10: Sick leave: A more appropriate legend would be work disability. Furthermore, there is a need for a brief explanation of the difference between sick leave and disability pension in the Swedish Social Insurance system (according to the regulations at the time of your study). Figure 6 only covers 2 years before and 2 years after the time of diagnose. This is not explained in the methods and why not 3 years? Authors reply: Thank you for valid suggestion on sick leave-work disability. In the last sentence page 6 paragraph work disability, we mention that we only have work disability data available for all subjects until 2 year post injury. Authors action: Legends Sick leave has been changed under the Methods section (page 7 line 1 and page 10 line 10), we now use the term Work disability. We have added more information on sick leave and disability pension page 10, line 10 and also in accordance with reviewer 3 moved the sentence where we mention that we only have work disability data up until 2 year post injury to the section Neck injury cohort. We hope this will better clarify our study period with respect to work disability. RESULTS Make sure that you write the p in p-value either with uppercase letter as in the abstract OR lowercase letter (preferable) as in the Results Section, not both Authors action: We agree, all uppercase P have been corrected as appropriate to lowercased p. Pp 11. Line 39. How is acute visit in primary care ascertained and defined? Is it acute or is it subacute? Have you any information about day of collusion? If not, it may be difficult to determine whether it is an acute visit or not? Authors reply: thanks you for this important question. In the register we can see whether the consultation was a priori scheduled or not. This is marked in the register as acute=yes/no. We have, unfortunately, no information on potential collision date.

13 Pp 12 Line It value that you have compared the low-frequent user and their transition into highfrequent user. However collapsing low-frequent and frequent consulters in the following results is a less good. These results are partly dependent on (influenced by) the first since low-frequent users constitute more than third of the collapsed group. I suggest that you isolate the frequent group, compare It to high-frequent users and present these results instead of the results from the collapsed groups. Authors reply: thank you for these suggestions. We agree that this is two groups that don t necessarily should be analyzed together especially since the low frequent consulter group is larger however; we did this because of the low number in totals. When we analyze the frequent group alone the attributable risk is 17.8%. Authors action: As suggested by reviewer 3, a new table including risk ratios and attributable risks for transition between groups and year have been added to the results section. Pp 15. Table 3. Preferable add information about the variance within groups. Can you comment on the results of the high-frequent group, with respect to the mean increase in number of consultations especially concerning psychological distress? ( you do so in the discussion but may well be reported in the Result Section) Authors reply: Thank you for this comment. On Page 15 line 7 we present the result over high prevalence s of psychological distress during the whole study period in the high frequent group. This is also discussed in the discussion section. We politely suggest not extending these sections. Pp 16 line 5. Replace the legend Sick leave, with Work disability Authors reply: Legend has been changed. Pp 16 line 7. This is not a case cohort study.it is better to phrase the first sentence.., 96 subjects of the cases (6.7%) were on.. Authors reply: Thanks you for pointing this out. Authors action: the sentence have been changed, it now reads: At the day of the neck injury diagnosis, 96 subjects of the cases (6.7%) were on disability pension, DISCUSSION PP18 Line: 15 I suggest a rephrasing of the sentence starting with Noteworthy,..in average about 16% developed a high-frequent consultation pattern that may be attributed to the injury. ( The results do not support your statement that this 16% persisted over at least 3 years You have calculated the mean over time (after injury but the curves in figure 5 shows a decrease after year 1 after the diagnosis.) Author s reply: Thank you for this comment; we agree that this sentence should be rephrased in order to better describe the pattern although the pattern seems to exist three years after injury. Please note, figure 5 displays the pattern over time stratified by pre-injury consultation level. Authors action: The sentence have been changed and it now reads (page 22, line 4): Noteworthy, about 16% of the transition from low or frequent consulters pre-injury to high-frequent consultation pattern the year after diagnosis could be attributed to the injury, and this pattern persisted, although slightly declining, up to at least 3 years. i) Pp18. Line 17. You state: However in a sub group of patients, high level of health care consultations were noted already long before the neck injury diagnosis. This implies that a individually tailored multimodal rehabilitation is and important tool in the care and recovery process of a subset of patients after neck injury None of the references cited (17, 22) really support this. On the contrary, if any, there are some evidence that multidisciplinary rehabilitation do not have an effect on recovery following WAD. Cassidy, J. D., L. J. Carroll, et al. (2007). "Does Multidisciplinary Rehabilitation Benefit

14 Whiplash Recovery?: Results of a Population-Based Incidence Cohort Study." Spine. Now, the study by Cassidy et al, did not specifically investigate the sub group of patients with massive health care consumption prior to an injury. Author s reply: Thank you for this comment and reference. We agree that the literature is not convincing on whether a multidisciplinary approach is the best, even if this particular article by Cassidy et al have a prolonged time before rehabilitation start which could be assumed affecting the results (median days 143). However, our study indicates that the background history of consultation is a proxy for ill-health. This is an aspect we suggest may be included in the treatment and rehabilitation of the patients regardless of disease or injury and regardless of type of rehabilitation. Author s action: We have chosen to delete the last sentence in the first paragraph under discussion; since it s not supported in our results. We have also included the suggested reference. Pp 19 Line: In reference 23,ONE possible reason for depression as a risk factor for WAD, may be an increased risk of collision due to the pre-collision mental conditions (poor concentration). However in the next sentence in that paper, the authors state that poor concentration is not likely to play a role in rear-end collisions. The way reference 23 is cited in your study is not completely correct. Authors reply: Thank you for highlighting this. We believe that this article suggests poor concentration as a risk factor for car collision in general. Hence, we don t mean to imply that this would be the case with rear-ending specifically. FIGURES Figure 5: Should be labeled months ( not month).. There is no explanation why you started 3 months prior to the diagnosis of neck injury and not 36 months as stated in the Method section. Authors reply: Thank you for this question and comments. We wanted to give the reader a possibility to see the change in months rather than in years in this figure. In order to facilitate this (simply to make the figure more readable), we started at 3 month before injury. Authors action: Month has been changed to months and the time-period has now been explained under the method s section. The sentence on the stratification on page 9 line 8 now reads: We used this categorization to perform stratified analyses. We present the numbers per year throughout with one exception; to study the number of consultations in detail after injury we display mean number of consultation within each subgroup by quarters of a year starting three months pre-injury. We have also pointed this out in the figure legend. Reviewer: Jordan Miller, School of Rehabilitation Science, McMaster University, Hamilton, Ontario, Canada Overall the study was well written, however, the manuscript would be strengthened by converting the use of the term 'neck injured individuals' to 'people with a neck injury' in order to use 'people first language'. Authors response: Thank you for this comment and the valuable suggestion on how to improve the language. We very much appreciate your expertise and careful input helping us to improve the manuscript. Authors action: We have changed the wording 'neck injured individuals' to 'people with a neck injury' throughout the manuscript. Page 1, Line 6: The word still is not necessary. Authors action: the word still has been deleted.

15 Page 1, Line 8: Tearing of should be replaced with injury to. There are many types of forces present in a whiplash injury, tearing implies shear and traction force, but I there are more possible explanations than tissue tearing. Authors action: We agree. The sentence have been rephrased and now read: The so called whiplash trauma mechanism may result in injury to several structures present in the neck Page 1 Line 15: pain sensitization needs definition. Perhaps this would be better stated as sensory hypersensitivity and if this statement is made, I think elaboration of tis prognostic indicator is needed (ex: pain pressure, cold hyperalgesia, locally vs. distally) Authors action: This sentence has been deleted, we found it added little to the introduction. L40-42: You describe prognostic indicators present before trauma and prognostic indicators at the time of trauma, but are there also post trauma prognostic indicators? Authors reply: We thank the reviewer for this important and interesting question. We believe there are post trauma prognostic factors, connected or not connected to the trauma itself. Besides these, factors like compensation certificates, type of treatment and beliefs have been shown both to improve and halter the rehabilitation process (Spearing 2012, Cassidy et al. 2007, Carroll et al. 2009) Authors action: In line with reviewer ones (1) comment on the terminology concerning trauma-related factors this terminology has been changed to post-trauma related health factors. Page 10, Line 50: Typographical error: 'rang sum' Authors reply: Thank you for mention this error. Authors action: We have in compliance with reviewer 3 deleted this sentence. In the discussion, the classification of the neck injury using S13 was discussed as a potential limitation. I think this is an important part of the discussion that should be elaborated upon. Authors reply: We agree. Authors action: We have further elaborated upon the uncertainty of the coding and limitation not knowing the true cause of the patients complaints; please see page 24, row 19.. i) In the introduction, the reader is led to think that people who's diagnosis is provided as S13 are primarily whiplash injuries. Is there evidence suggesting this is how whiplash injuries are coded? Authors reply: Thank you for this important question. We have used the ICD-10 code recommended to use in relation to a whiplash trauma to the neck. S134 include S134A-C, A=Whiplash injury WAD 1, B Whiplash injury WAD 2 and Whiplash injury WAD 3. However, we discussed the coding procedures both with primary care practitioners and with pain specialist and we came to the conclusion that S13.4 should be used in whole since most of the coding still is done without using A-C classification. This is also what s been done in previous studies and investigations in Sweden. However, there are other codes that could be used, late whiplash injury and other like S14.0 Concussion and oedema of cervical spinal cord, S24.1 Other and unspecified injuries of thoracic spinal cord however these are not the common codes to use. ii) Is 'sprain or strain' of the neck the most appropriate description of a traumatic neck injury. Authors reply: We agree that this might not be the best word to use, however this is the wording used in the international version of ICD10, S13.4. Authors action: We comply with your comment and have changed our terminology to neck injury throughout. The sentence under subheading neck injury cohort page 7 now reads: We identified all adult (18 years or older) residents of Region Skåne who had been diagnosed with neck injury, Whiplash, ICD-10-SE code S13.4*, iii) In the ICD-10 CA WAD 1-3 are classified as S1340-S1342. Were these classifications not available for the physicians who are making the diagnosis?

16 Authors reply: We thank you for this question. We appreciate that this is not described properly in our manuscript. In the Swedish version S134 include S134A-C, as the CA version include 0-2, where A-C equals whiplash injury WAD 1-3. Author action: To better describe the diagnostic codes used in our study we have added information about how S134 is built up in the Swedish version of ICD-10. We have inserted a new sentence on this on page 7, line 22 that read: S13.4 is in the Swedish ICD-10 version further subdivided for Whiplash associated disorder (WAD) 1-3, by the letter A-C (i.e., S13.4A). Please see also our reply to i) above. iv) Why was the analysis performed on S13 and S16, S130, S142, etc. were not included? This is not meant to criticize the decision to use only this classification, but I think it is important that the reader understand the rationale for the decision. Also, if S13 is being used to try to target traumatic neck injuries with a whiplash mechanism, sufficient evidence is needed to suggest that S13 is made up of primarily whiplash injuries. Otherwise, this may need to be reframed to suggest the population represents 'people who were diagnosed by their physician as having a sprain or strain of the neck. Authors reply: We were primarily interested in the whiplash injury mechanism, and that is why we focused on those particular ICD-10 codes. However, due to the observational nature of the study including some uncertainty of the physicians coding practice etc.; we do not know that all patients have been truly exposed to a whiplash trauma. Hence, we fully agree with the reviewer s comment, and hope that this has been accurately conveyed in the limitations section (page 24 lines 19-24). Reviewer: Daniel Pinto Assistant Professor, Department of Physical Therapy and Human Movement Sciences/Center for Healthcare Studies, Feinberg School of Medicine, Northwestern University USA I have no competing interest We thank the expert reviewer for his very helpful input on our manuscript Description of methods: There could be a more precise reporting of methods which would specific in greater detail which statistical tests were performed with a given variable. All of the statistical tests were reported but it would have been helpful to know whether in a given situation the researchers were comparing count data versus proportions. Authors reply: Thank you for this important comment, we agree that a more precise description would facilitate for the reader and also that better statistical methods taking the underlying distribution into account in better ways. Therefore substantial changes have been made concerning the analysis hence also the statistical analysis section. We have included risk ratios in combination with the attributable risks, and Jonckheere-Terpstra test when analysing differences between patients with neck injury to the references. Lastly we have, as suggested, included repeated negative binominal regression models to study the difference between subgroups taking other variables into account. Authors action: We have updated the whole Statistics analysis section and changed the analysis accordingly, starting on page 10. Also, it was unclear whether there was justification for use of t-tests with count data. This would require that a large number of levels were present in the data. Author s reply: thank you for pointing this out. We agree and think this is a valid point. Authors action: We have made major changes regarding our statistics; we now include t-test, Mann- Whitney U-test and median tests, Jonckheere-Terpstra. We do however correlate number of consultations with number of sick days; therefore we have added Fischer s z transformation to compute 99% CI around the correlation coefficient. This is explained in the statistics section starting

17 on page 10. the results section is lacking organization Authors reply: We appreciate your suggestions (below) and have revised the results section accordingly. The conclusion that consultation history be taken into account when tailoring individual treatment seems premature considering there was no discussion about how this might happen. In fact, the study doesn't discuss optimal health care use at all which may fall somewhere between the low users and high users. Authors reply: Thank you for highlighting this aspect. We agree that this part of our conclusion is premature and agree that the best way at this stage is to delete the sentence. Authors action: The sentence has been deleted. The authors should be congratulated for their work. They have carried out a well-conducted casecontrol design assessing health care consultation and sick leave before and after neck injury. They used four matched controls per case with sensitivity analyses based on matched variables. However, this paper makes for difficult reading on account of poor organization and a lack of clarity concerning methodology. Authors reply: We appreciate you positive comments on our work and are thankful for your questions, comments and suggestions to help us improve the paper. Specific comments: Pages 2-3 Abstract: Objectives: could introduce rationale from line 1 page 4 into objectives in abstract providing reader with context of study. Authors reply: Thanks you for this good suggestion. Authors action: Due to word limitations the the objectives in the abstract now read: Recent studies, based on self-assessed data both on exposure and outcome, suggest a negative association between poor health before neck injury and recovery. Our aim was to study actual health care consultation and work disability before and after neck injury (whiplash). Conclusions: It is not clear how consultation history should be taken into account. Unless authors propose some suggestions as to how this might be realized, I suggest this statement be altered. Authors reply: We appreciate this suggestion and agree. Authors action: We have deleted this section. Page 4 Article summary: Strengths and limitations: Potential misclassification bias toward showing less difference between groups... This was not well discussed in the limitations section of the article. How do the authors suggest this might produce this bias? This requires further explanation in the discussion section to earn inclusion in the summary. Authors reply: Typically non-differential misclassification of an exposure (which we believe is the case here) will bias estimates towards the null, i.e. making it harder to detect true differences between groups. With word count in interest we choose not to elaborate on this further in the discussion. Authors action: We have deleted part of the limitations section under the summary, it now reads: A limitation of the study is potential misclassification of injury although the injury code used to identify cases primarily is connected to the whiplash injury mechanism; other trauma mechanisms may be included as well. Page 5, Introduction, top of the page, line 0 the sentence beginning with the so called whiplash...