Title:The epidemiology of hospital treated traumatic brain injury in Scotland

Transcription

1 Author's response to reviews Title:The epidemiology of hospital treated traumatic brain injury in Scotland Authors: Tara Shivaji Andrew Lee Nadine Dougall Thomas McMillan Cameron Stark Version:2Date:25 November 2013 Author's response to reviews: see over

2 Nadine Dougall, Lecturer Iris Murdoch Building University of Stirling Stirling FK9 4LA Tel: +44 (0) Fax: +44 (0) st October 2013 Dear Editor, MS ID#: MS TITLE: The epidemiology of hospital treated traumatic brain injury in Scotland Please find uploaded a word document of the revised manuscript bearing the title above. We are grateful for the comments of the reviewers, whose constructive commentary proved helpful in improving the content of the paper. A table outlining reviewer comments along with our responses follows on the next page. We have inserted a statement to address the query about the ethics committee approval; ethical review was not needed as the data were used as part of service evaluation and not empirical research; we have now clarified this in the manuscript. Finally, we have formatted the manuscript throughout to conform to your journal style. Yours sincerely, Nadine Dougall NMAHP Research Unit is funded by the Chief Scientist Office, Scottish Government Bases at: Glasgow Caledonian University and University of Stirling The University of Stirling is a charity registered in Scotland, number SC Glasgow Caledonian University is a charity registered in Scotland, numbersc O21474

3 Reviewer 1 comments 1.1 This manuscript shows that there is an increase in hospitalization for TBI in the >65yo population in Scotland; with different trends depending on the time periodin the last 12 years. However, it is difficult or impossible to discern from the data whether it is due tomore severe injuries (are only severe injuries hospitalized and the other onesdischarged home), or to socioeconomic condition of that population (for the sameinjury in 2004 now because of lack of support at home those people arehospitalized), or to an aging population (total incidence of TBI seen vshospitalized). 1.2 As noted by the author one of the major limitation of the study is "the interpretation of these findings" - but without interpretation it is merely an epidemiologicalpaper. Our response The reviewer has pointed out an important consideration of the study; we have amended the text in the discussion so it now reads: Several limitations of the study methodology require consideration in the interpretation of these findings. One limitation concerns underreporting of less severe TBI. As is common with all routine hospital datasets, the SMR01 hospital dataset only identifies the individuals who seek care. People who sustain injuries during sporting activities, as a result of domestic violence, whilst under the influence of alcohol or drugs are less likely to seek care of any form [13]. Not all people who present to accident and emergency departments are onwardly admitted to hospital. We agree that we could do more to interpret the findings of the paper for instance make more of figure 1 results. We said: Several limitations of the study methodology require consideration in the interpretation of these findings, then we next set out these limitations to contextualise the summary data by pointing out that the hospital datasets don t include individuals who self-care or actively choose to not seek care, or who attend Emergency Departments, primary care or private facilities - but are not onwardly admitted to general hospital. This is not quite the same as saying that the interpretation of these findings are a major limitation nevertheless we agree that we could make more of guiding the reader in interpreting the data (see below). In the introduction we stipulated that there was a need for an improved understanding of the epidemiology of TBI in Scotland so that measures to prevent and treat the burden of morbidity can be developed and evaluated. Therefore our primary aim was to produce epidemiological data for TBI hospitalisations. We have added reference to the limitations of the 2

4 method, and have included greater reference to studies in other countries to provide more context for the reader. Reviewer 2 comments Our response 2.1 This study primarily studies trends in hospitalizations by age and gender over atwelve year period using routinely collected hospital data. The focus on age andgender is important and addresses a research gap in this area. Abstract Is fairly clear but could be reorganized better. The last sentence of thebackground may be better put after first sentence Methods: grammatical issues..should be analysis were used. Results: the first sentence is not compete 2.2 Introduction The author cites relevant references such as systematic reviews. However, thereare many more recent papers citing more up to date TBI rates which are higher than those cited. Also comparisons to other publicly insured populations could bemade in both introduction and discussion. We agree and have rearranged the sentences as suggested. Corrected. Corrected. We undertook a literature search focusing on more recent papers. We have added several references to additional work in the US, Canada, Scandinavia and Australasia, which we felt were comparable contexts. We agree that this improves the paper. 2.3 I believe the rationale for using the CDC definition should go in the methods section of the paper. 2.4 Although the aims of the paper are to estimate incidence, the paper is reallyabout hospitalizations or episodes of care. The authors cite in fact that a smallnumber of readmissions are included in the analyses. We agree and have rearranged the text as suggested. We agree this is an important point for clarification, the hospitalisation incidence as a result of TBI is not the same as the TBI incidence. We checked the text throughout the manuscript to ensure that incidence referred to hospitalisation incidence as a result of TBI, and amended the methods section to read as follows: Individual discharge records were combined during analysis to identify periods of continuous hospital care so that the combined records for each person 3

5 from admission with TBI to discharge home were counted as one continuous episode; for instance a transfer from the care of one Consultant to another, or a discharge from a general hospital setting to rehabilitation facility was counted as one episode of care. It is possible that the same individual could have been admitted more than once, so the study is therefore a description of continuous care episodes rather than the number of affected individuals. For additional transparency, we have also provided text about this in the discussion section on study limitations: It is also important to note that the figures are for continuous hospitalisation episodes after TBI, and it is possible for one individual to have had more than one admission. We made other amendments to text and headings to make this as clear as possible. 2.5 Methods The author uses a statistical technique that is not typically seen in trend studiesin the TBI literature. As such I believe the authors could highlight more this novelcontribution. The technique has been cited in the literature. We thank the reviewer for making this point. We have inserted the following additional text into the methods section to highlight the novel use in TBI and also by way of explanation the origins of Joinpoint statistical software: Joinpoint software has a specific application for trend analysis where data do not appear to be represented by a single regression slope, but instead are represented by a series of linear segments connected at joinpoints or elbows in the data with joinpoints being typically marked in time by years where the trend appears to have altered. Joinpoint is used extensively in the analysis of cancer trend data and is freely available to download for use from the US National Cancer Institute website ( Although Joinpoint has primarily been used in cancer research, it has crossed over into widespread use in trend analysis in other areas, for example stroke (Bajaj 2010), heart disease (Nichols 2013), chronic obstructive pulmonary disorder (Lopez-Campos 2013)and suicide (Thomas 2011, Stark 2008). 2.6 Did this study proposal undergo ethics review? The work was initially conducted on behalf of the Scottish Acquired Brain Injuries Network in their 4

6 work on service review in Scotland. We took advice from the NHS Highland Research and Development office, who discussed the matter with the scientific officer of the relevant Ethics Committee, and they advised that Research Ethics Committee approval was not required. We have inserted the following text into the Methods section to clarify: This study was conducted as part of a service evaluation project and did not require ethical review. The study used anonymised, routinely collected data which was held by the Information and Statistics Division (ISD) of NHS Scotland. Approval from the Privacy Advisory Committee at ISD was not required, as no new linkage was required. 2.7 Results: The authors should label where the in the results the figures and tables would beplaced Table 1 refers to the ICD 10 codes used to identify TBI and is now cross-referenced in the methods section. Tables 2 & 3 and figure 1 are all referred to in the results section next to the relevant text in the results section; additional cross-referencing has now been made. With respect to the tables, the confidence intervals for the results are quite largeand include 0 while having significant p values. This warrants further discussion. Some figures of trends may highlight results better. 2.8 Discussion Valid points are made. However they also miss issues regarding practicepatterns to explain results which have been cited as explaining trends in studieson trends especially as it relates to age. There is mention of trends in thepediatricpopulation but could be better linked to results. Whereas the 95% confidence intervals in Table 2 refer to the annual percentage change, the p-values are not referring to the APC, but instead relate to the likelihood that the estimated number of joinpoints is true compared to the null hypothesis of zero expected joinpoints. We have now clarified this in the footnotes of table 2 and table 3. We were not able to produce this figure as the first author has since moved abroad and did not have relevant permissions to transport the dataset outside of the UK. We have added additional references to make the point that changes in admission patterns could result from changed clinical practice, particularly in relation to mild brain injury. We have also added references specifically on paediatric brain injury. 5

7 More could be said about the implications of these results including mechanismsof injury eg assault and methodological issues. We have added relevant references on methodology, which we agree have improved the paper. We have also added a specific reference to violence in the Conclusions. Reviewer 3 comments 3.1 I think this is an interesting study on TBI epidemiology of hospital-treated TBI inscotland. The title and abstract accurately convey what has been found. The study aims are well defined and the methodology is appropriate. The major limitations of the study are clearly stated. Our response However, there are some issues that might be addressed in order to improve thepaper, see below. The population base and referral criteria for TBI hospital admissions in Scotlandis lacking. 3.2 The introduction and discussion does not integrate well the findings from recentstudies on incidence of hospital-treated TBI. More precisely, the referred reviewby Tagliaferri et al. includes studies published from 1980 to 2003 while this studydescribes the TBI hospitalizations from 1998 to There have been trendchanges in the incidence of TBI hospitalizations during the last decade, and it ismore relevant for this paper to refer to the newer incidence publication from theus, Netherlands and Scandinavian countries. We have added a brief description of the health system in Scotland, which we hope will be helpful for international readers. We have also added a reference to the current Scottish guidelines on brain injury treatment. We have added more recent studies from the US, Canada, Scandinavia and Australasia to the discussion. These related well to our findings, and we think that their inclusion has improved the paper. 6