COGNITIVE SYMPTOMS are common in individuals with

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1 1774 ORIGINAL ARTICLE Validity and Reliability of the Perceived Deficit Questionnaire to Assess Cognitive Symptoms in People With Chronic Whiplash-Associated Disorders Hiroshi Takasaki, MSc, Chi-Wen Chien, PhD, Venerina Johnston, PhD, Julia Treleaven, PhD, Gwendolen Jull, PhD ABSTRACT. Takasaki H, Chien C-W, Johnston V, Treleaven J, Jull G. Validity and reliability of the Perceived Deficit Questionnaire to assess cognitive symptoms in people with chronic whiplash-associated disorders. Arch Phys Med Rehabil 2012;93: Objective: To investigate the validity and reliability of the Perceived Deficit Questionnaire (PDQ) for use in people with chronic whiplash-associated disorders. Design: Cross-sectional. Setting: Tertiary institution. Participants: Patients (N 105) with chronic whiplash-associated disorders and asymptomatic controls (n 50). Interventions: Not applicable. Main Outcome Measures: The 20-item PDQ inclusive of 4 sections (attention/concentration, retrospective memory, prospective memory, and organization/planning) rated on a 5-point scale. Results: Internal construct validity of the PDQ was examined by Rasch analysis, confirming the appropriateness of its 5-point scale and the unidimensionality of each section after modification by eliminating 1 item each from the attention/concentration and retrospective memory sections. Preliminary evidence was also gained for external construct validity (convergent validity) of the modified PDQ by demonstrating significant (P.05) correlations of all sections with a global measure of disability due to neck pain (the Neck Disability Index). The whiplash group demonstrated significantly (P.05) higher scores in each section of the modified PDQ than did the control group, indicating evidence for discriminant validity. In addition, the modified PDQ demonstrated good internal consistency (Rasch-generated reliability.8) and acceptable test-retest reliability with 1-month interval (intraclass correlation coefficients.8). Conclusions: The modified PDQ appears to be a valid and reliable questionnaire and could be used quickly in clinical practice to gain a basic understanding of perceived cognitive symptoms in people with chronic whiplash-associated disorders. Key Words: Cognition; Neck pain; Questionnaires; Rehabilitation; Reproducibility of results; Whiplash injuries by the American Congress of Rehabilitation Medicine From the National Health and Medical Research Council Centre of Clinical Research Excellence Spinal Pain, Injury and Health, Division of Physiotherapy (Takasaki, Johnston, Treleaven, Jull) and the Occupational Therapy Division (Chien), School of Health and Rehabilitation Science, The University of Queensland, Brisbane, Queensland, Australia. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Correspondence to Hiroshi Takasaki, MSc, CCRE Spine, Division of Physiotherapy, School of Health and Rehabilitation Science, The University of Queensland, Brisbane, Queensland 4072, Australia, h.takasaki@uq.edu.au. Reprints are not available from the author. In-press corrected proof published online on Jul 14, 2012, at /12/ $36.00/0 COGNITIVE SYMPTOMS are common in individuals with chronic whiplash-associated disorders (WAD), 1-5 although physiologic evidence of brain injuries has not been found in those with cognitive symptoms. 6 The mechanisms of cognitive symptoms remain unclear in this population. However, a reduction in cognitive skills associated with chronic WAD could be associated with pain, psychological stress, and/or side effects of medications used for pain control. 7 To identify the mechanisms of cognitive symptoms, it is first necessary to have a psychometrically sound self-rating questionnaire that assists understanding of the degree of cognitive symptoms perceived by individuals with chronic WAD. Such understanding would facilitate the development of relevant clinical tests and treatments for these patients as may be necessary. Of existing questionnaires to assess levels of perceived cognitive symptoms, 5,8-12 the Perceived Deficits Questionnaire (PDQ) is of interest as it includes a broader range of cognitive domains. Its clinical usefulness was demonstrated by Sullivan et al 5 in a preliminary study. Individuals with chronic WAD were found to have greater perceived cognitive symptoms than asymptomatic individuals. Therefore, the PDQ may have potential for use with chronic WAD. However, the suitability of the PDQ has not been tested, nor has comprehensive psychometric testing been undertaken. The purpose of this study was to investigate the validity and reliability of the PDQ in individuals with chronic WAD. METHODS Perceived Deficits Questionnaire The PDQ was originally developed for patients with multiple sclerosis. 13 It consists of 4 sections attention/concentration, retrospective memory, prospective memory, and organization/ planning. Each section has 5 items listing different cognitive complaints. Respondents rate the frequency of each complaint on a 5-point Likert scale anchored from never (0) to almost always (4). Each section is scored out of 20, and higher scores are indicative of more disabilities. Participants and Data Acquisition Procedures A convenience sample of 105 individuals with chronic WAD was recruited from patients attending a university whiplash clinic, via advertising in the public press and referral from health practitioners in the community in an Australian setting. The sample could by definition be categorized as WAD grade MnSq NDI PDQ WAD Zstd List of Abbreviations mean square Neck Disability Index Perceived Deficits Questionnaire whiplash-associated disorders standardized Z value

2 COGNITIVE SYMPTOMS IN CHRONIC WHIPLASH DISORDERS, Takasaki 1775 II or III on the Quebec Task Force classification. 14 Participants were aged between 20 and 60 years. They had ongoing neck pain related to a whiplash injury sustained in the last 3 months to 5 years. Exclusion criteria were a history of unconsciousness at the time of the whiplash injury, a diagnosed cervical fracture or dislocation (ie, WAD grade IV), or a comorbid neurologic disorder (eg, multiple sclerosis). The WAD participants completed (1) a general survey to provide information on demographics and symptom duration, (2) the PDQ, (3) a0to10numerical Rating Scale for current neck pain intensity, and (4) the Neck Disability Index (NDI). 15 Twenty-five of the 105 participants agreed to complete the PDQ again 1 month after the first administration to examine the test-retest reliability of the PDQ. Fifty asymptomatic individuals without any history of whiplash injury were recruited from a local university as a control group. Those with any history of diagnosed mental problems or neurologic disorders were excluded. Control participants completed the PDQ and the general survey on demographics only. Surveys could be completed online or as paper-based surveys, according to the individual participant s preference. Ethical clearance for the study was gained from the institutional human medical ethics committee, and all participants provided informed consent. Statistical Analysis Data analysis was conducted in 3 stages to examine the PDQ in terms of its internal and external construct validity and test-retest reliability. First, the internal construct validity was assessed using Rasch analysis, an increasingly popular analysis method to examine the validity of assessment tools Rasch analysis focuses on investigating the interaction between person ability and item difficulty in a given test. Person ability is reflective of the latent trait to be measured by the items (perceived cognitive symptoms in this study). In the PDQ, an individual with a score of 10 in a certain section is expected by the Rasch model to have greater disabilities than an individual with a score of 0. These individuals can be further placed in a hierarchical order on the basis of their cognitive symptoms within the Rasch model s expectations. Likewise, the items in a test can be placed from easy to difficult on the basis of item difficulty, which is an estimate of an item s underlying difficulty calculated from the probability of the individuals who succeed on that item. A PDQ item with a higher item difficulty would be expected to reflect greater disability because the PDQ items use negatively scored response formats (ie, higher ratings indicate higher levels of cognitive symptoms). With Rasch model s expectations, 3 aspects of internal construct validity of the PDQ were examined on the basis of the rating scale model. 23 The first aspect was to investigate the appropriateness of the response format of each PDQ section, because inappropriate response format can lead to a skewed distribution of test scores that may further affect the PDQ s internal construct to reflect the magnitude of perceived cognitive symptoms. The response format was considered appropriate when (1) any response option had at least 10 counts, (2) average measures of person abilities increased with response options, (3) outfit mean square (MnSq) values of each response option were no more than 2, and (4) there was no disordering step calibration (ie, the difficulty level of a lower step [eg, between the never (0) and rarely (1)] was higher than that of its adjacent higher step [eg, between the rarely (1) and sometimes (2)]). 24 The response options were collapsed if such criteria were not satisfied. The second aspect was related to the examination of the unidimensionality of each PDQ section (ie, whether items in each section measure a single construct). The Rasch principal component analysis 25 was used to examine the unidimensionality of each PDQ section. In principal component analysis, the eigenvalue size of 2 in the first contrast (which is the largest secondary dimension/component after the Rasch-derived construct is removed) has been proposed as a cutoff value to indicate that there is no multidimensionality in the test items. 26 Subsequently, the goodness of fit of the PDQ items in each section was also examined using infit and outfit statistics to detect the items threatening a test unidimensionality. 16 The infit MnSq is sensitive to the ratings on the PDQ items located close to the person s ability, whereas the outfit MnSq is more influenced by the ratings on the off-target items (ie, items for much more or much less severe than the participants cognitive symptoms). 25 The MnSq value can be further transformed to a standardized Z value (Zstd). An item with MnSq 1.4 and Zstd 2 indicates that such an item reflects a different construct from other items (ie, misfitting), whereas an item with MnSq 0.6 and Zstd 2 indicates a redundant item (ie, overfitting). Such misfitting items were excluded from the PDQ in a stepwise manner until all retained items demonstrated acceptable fit criteria. Overfitting items were retained as these items do not affect unidimensionality. The third aspect in relation to internal construct validity is the response distributions of each section. Floor and ceiling effects were examined by investigating the percentage of participants who achieved the lowest and highest scores in each PDQ section. A threshold of 15% was used similarly to a previous study. 27 In addition, Rasch analysis generated an item-person map in which the PDQ items were placed in a hierarchical order on the basis of item difficulty against the participants being arranged hierarchically on the basis of person ability, along the same scale. The item-person map was inspected visually to investigate item suitability for people with chronic WAD (ie, item-to-person targeting). Second, the external construct validity was assessed. Particularly, this study examined convergent validity by investigating the relation between the score for each PDQ section and the NDI scores, which is a global measure of disability. In addition, the relation between the score for each PDQ section and participants age and neck pain intensity was investigated to better understand psychometric properties of the modified PDQ because these 2 factors are important in considering cognitive abilities. Scores in each PDQ section were compared between the chronic WAD group and an asymptomatic group to investigate discriminant validity. The Spearman correlation and the Mann- Whitney U tests were used, as data on the 105 whiplash participants were not normally distributed in the Kolmogorov-Smirnov tests. The significance level was set at P.05. Third, test-retest reliability of each item and section was investigated after a 1-month interval. The quadratic weighted was used at the item level. At the section level, intraclass correlation coefficient was used because a normal distribution of the 25 whiplash participants data was confirmed by Shapiro-Wilk tests. All analyses except for Rasch analysis were performed using SPSS version a The Winsteps version b was used to perform Rasch analysis. A minimum sample size of 50 participants is required for Rasch analysis, 24 but it is more generally accepted that at least 100 participants with varied characteristics can produce precise Rasch analysis estimations. 25,28 Therefore, the sample size of 105 participants recruited in this study could be considered sufficient. RESULTS Participants Demographics for the total whiplash group (N 105), the subset of 25 whiplash subjects undertaking the test-retest reliability, and the control group are presented in table 1. Partic-

3 1776 COGNITIVE SYMPTOMS IN CHRONIC WHIPLASH DISORDERS, Takasaki Variables Table 1: Participant Demographics Total Sample (n 105) Chronic WAD Reliability Study Sample (n 25) Asymptomatic Control (n 50) Age (y) * Symptom duration (mo) NA.73 NDI NA.93 Current neck pain on 0 10 Numerical Rating Scale NA.15 Women 84 (80) 21 (84) 32 (64).07 NOTE. Values are expressed as mean SD or n (%). Abbreviation: NA, not applicable. *One-way ANOVA, post hoc analysis with Bonferroni adjustment demonstrates the following: P.52 (chronic WAD total sample versus chronic WAD reliability study sample); P.03 (chronic WAD reliability study sample versus control); and P.14 (chronic WAD total sample versus control). Independent sample Mann-Whitney U test, chronic WAD total sample versus chronic WAD reliability study sample. Independent sample t test, chronic WAD total sample versus chronic WAD reliability study sample. 0 indicates no pain, and 10 indicates pain as bad as it could possibly be. Fisher exact test. P ipants with chronic WAD demonstrated moderate disability due to neck pain. 15 There was no difference (P.05) in demographics between the total whiplash group, the subset used to examine test-retest reliability, and the control group. Internal Construct Validity In each PDQ section, the response format was considered appropriate according to the predetermined criteria (table 2). Consequently, no rescale of the 5-point response format was made. In terms of unidimensionality, the principal component analyses did not reveal any sufficient eigenvalue in 3 of the 4 PDQ sections as other obvious factors in addition to the Rasch-based component (ie, attention/concentration 1.7, prospective memory 1.6, organization/planning 1.9). However, a potentially sufficient eigenvalue (ie, 2.0) was found in the retrospective memory section, indicating a sign for multidimensionality. Further item-fit analysis found that in the retrospective memory section, item 6, I have difficulty remembering the names of people even if I have met them several times, exhibited misfitting criteria (infit MnSq 1.48, infit Zstd 3.1, outfit MnSq 1.46, outfit Zstd 3.0). In the attention/concentration section, item 5, I have trouble holding telephone numbers in my head, even for a few seconds, did not satisfy the fit criteria (infit MnSq 1.84, infit Zstd 5.0, outfit MnSq 1.84, outfit Zstd 4.9). Considering their threat to unidimensionality, these 2 items were eliminated from the relevant sections and the Rasch analysis was rerun. Table 3 shows that all remaining items demonstrated acceptable fit criteria. Unidimensionality was confirmed by the principal component analyses in retrospective memory (eigenvalue 1.8) and attention/concentration (eigenvalue 1.6) sections in the modified PDQ (with items 5 and 6 Table 2: Investigation of the Appropriateness* of the 5-Point Likert Scale in Each PDQ Section Using the Rasch Analysis Based on Rating Scale Model PDQ Sections Rating Category Category Count (%) Average Measure Outfit MnSq Calibration Attention/concentration Never None Rarely Sometimes Often Almost always Retrospective memory Never None Rarely Sometimes Often Almost always Prospective memory Never None Rarely Sometimes Often Almost always Organization/planning Never None Rarely Sometimes Often Almost always *The response format was considered appropriate when (1) any response options had at least 10 counts, (2) average measures of person abilities increased with response options, (3) outfit MnSq values of each response options were no more than 2, and (4) there was no disordering step calibration (ie, the difficulty level of a lower step was higher than that of its adjacent higher step).

4 COGNITIVE SYMPTOMS IN CHRONIC WHIPLASH DISORDERS, Takasaki 1777 Table 3: Fit Statistics in the Modified PDQ* Items (Item Number and Description) Measure SE Infit MnSq Infit Zstd Outfit MnSq Outfit Zstd Attention/concentration 1. I lose my train of thought when I am speaking During conversation, I have difficulty concentrating on what people are saying I have trouble concentrating on things like watching a television program or reading a book I find that my mind tends to drift a lot Retrospective memory 7. I can t remember if I have already done something I can t remember what I did the night before After a telephone conversation, I can t remember what we talked about I can t remember what I did last weekend Prospective memory 11. I forget what I came into the room for I miss appointments and meetings I ve scheduled I can t remember the date without looking it up I forget to do things like turn off the stove, or turn on my alarm clock I forget to take my medication Organization/planning 16. I have trouble getting things organized I have difficulty planning what to do during the day Even though I have a lot of things to do, I have a lot of trouble getting started At times, it seems like my mind goes totally blank I have trouble making decisions Acceptable fit statistics require 0.6 MnSq 1.4 and 2 Zstd 2. *Items 5 and 6 have been excluded. withdrawn). All items in the prospective memory and organization/planning sections satisfied acceptable fit criteria (see table 3). The Rasch-generated person separation index values, the interpretation of which is similar to Cronbach s alpha, were.87,.85,.80, and.87 in the attention/concentration, retrospective memory, prospective memory, and organization/planning sections, respectively. These values indicate an acceptable level of internal consistency in each section of the modified PDQ. 29 As for response distributions, no section of the modified PDQ revealed either floor effects (3.8% 6.6%) or ceiling effects (0%). For item-to-person targeting, the Rasch item-person maps based on difficulty estimates for each step threshold of the 5-point scale (fig 1) showed that the means of person ability were negatively deviated from the means of item difficulty in every section of the modified PDQ but the modified PDQ items difficulty levels appeared to encompass most people with chronic WAD. However, figure 1 demonstrates the gaps between items for all sections. In particular, the prospective memory section had a large gap between the group of items 11 and 13 and the group of items 12, 14, and 15. External Construct Validity Table 4 documents the correlation coefficients between each section of the modified PDQ and variables of age, the 0 to 10 Numerical Rating Scale, and the NDI. Each PDQ section demonstrated statistically significant (P.05) correlations with NDI scores, suggesting convergent validity of the modified PDQ in people with chronic WAD. The attention/concentration and organization/planning sections had statistically significant (P.05) correlations with the 0 to 10 Numerical Rating Scale. In addition, the prospective memory section showed a significant correlation with age (P.05). In contrast, there was no significant correlation between retrospective memory and age (P.05). In addition, scores in the whiplash group were significantly higher than those in the control group across all sections with Cohen s d 0.4 (table 5), indicating discriminant validity. Test-Retest Reliability Table 6 provides the test-retest reliability for each item and each section of the original and modified PDQs. Only 1 item, I forget to take my medication, demonstrated poor test-retest reliability (weighted.4). 30 However, the test-retest reliability for each section of the original and modified PDQs (.79 intraclass correlation coefficient.83) was considered acceptable for people with chronic WAD. 30 DISCUSSION To our knowledge, this is the first study to investigate the internal construct validity, external construct validity, and testretest reliability of a self-reporting questionnaire for cognitive symptoms in people with chronic WAD. This study confirmed that the modified PDQ is a valid and reliable tool to use in this group to gain a basic understanding of perceived cognitive symptoms. Therefore, the modified PDQ may be used as a quick method by clinicians to assess clients cognitive problems to plan client-centered interventions and might also be used for monitoring recovery. With respect to internal construct validity, Rasch analysis demonstrated that the PDQ s 5-point Likert scale was appro-

5 Attention/Concentration* Retrospective memory* Prospective memory Planning/Organization PERSON - MAP - ITEM <greater disability> <frequent> 8 XX 7 Item 4 X XX Item 4 3 XX Item 2 Item 1 2 XXXXX Item 3 1 XX 0 M Item 4-1 M Item 2-2 Item XXXXX Item 3 XXXX XXX -5 XXXX -6 XX 0-1 Item 4 Item 2-7 XXXXXXX Item 1 Item 3 <less disability> <rare> Item 2 Item 1 Item 3 PERSON - MAP - ITEM <greater disability> <frequent> XX XXXX X Item 7 2 XXXXXXX Item XXX M -1 XXX Item 7 X Item 10-2 M -3-4 XXXXX Item 7 XX -5 Item 10 XXXXX Item XXXXXXX <less disability> 0-1 Item 9 <rare> 1-2 Item 8 Item Item 8 Item Item 7 Item 10 Item 8 Item 9 PERSON - MAP - ITEM <greater disability> <frequent> XXXXXXX Item 11,13 Item 14,15 XXX Item 11,13 Item 12 XXXX XX Item 15 Item 13 // Item 14 0 XXX M Item 11 Item 12 XXXXXX -1 XXXXX M Item 11,13 // Item 15-2 Item 14 XXXXX Item 12 XXX -3 XXX -4 XXXXXXX -5 X <less disability> 0-1 Item 15 Item 14 Item 12 <rare> PERSON - MAP - ITEM <greater disability> <frequent> 6 5 Item 18 Item 19, 20 4 X Item 16 3 XXX X Item 17 2 XX Item 18,19,20 1 XX XXXX X 0 M XXXXXX -1 M XXX Item 18 Item 19,20-2 XXXXXXX -3 XXXXXXX -4 Item 18 Item 19,20 XXXXXX Item 16 XXXX -5 Item 17 XXX -6 XXXXX <less disability> 0-1 <rare> 1-2 Item 16 Item Item 16 Item COGNITIVE SYMPTOMS IN CHRONIC WHIPLASH DISORDERS, Takasaki Fig 1. Item-person maps of the PDQ with step thresholds of the 5-point rating scale measures. Higher positive values indicate people with more cognitive disability and more frequent cognitive complaint items. * indicates that 1 item has been removed from the section, and each X indicates 1 participant.

6 COGNITIVE SYMPTOMS IN CHRONIC WHIPLASH DISORDERS, Takasaki 1779 Table 4: Spearman Values Between Each Section of the Modified PDQ and Age, Current Neck Pain Intensity, and NDI Scores Sections of the Modified PDQ Age Spearman (P) 0 10 Numerical Rating Scale Attention/concentration.11 (.28).31 (.001).50 (.001) Retrospective memory.14 (.17).10 (.32).26 (.01) Prospective memory.20 (.04).17 (.09).32 (.001) Organization/planning.02 (.86).25 (.01).35 (.001) priate for this group. Rash analysis also pointed to the need for some modification of the PDQ to ensure the unidimensionality of each section by excluding 2 items threatening the unidimensionality for the attention/concentration section and the retrospective memory section when used in the chronic whiplash population. Item 5, I have trouble holding telephone numbers in my head, even for a few seconds, exhibited misfit with the other 4 attention/concentration items. An expression such as holding in my head for a few seconds might have potential for reminding respondents of a memory skill. The developers of the PDQ appeared to have categorized this item into the attention/concentration section without testing its dimensionality. Thus, further assessment is required to categorize this item into the most suitable dimension or to reword its description if this item retention in the attention/concentration section is preferred (eg, I have trouble holding telephone numbers in my head ). Similarly, item 6, I have difficulty remembering the names of people even if I have met them several times, was misfitting in the retrospective memory section. When responding to this item, respondents may be affected by other factors, whereas the responses are straightforward for the other 4 items in this section. For example, the importance of the person to the respondent may affect the memory of that person s name. Thus, exclusion of the 2 items on the basis of Rasch analysis results might enhance the preciseness of the unidimensional construct in these 2 sections. With the preliminary evidence at this point, the use of a modified PDQ appears preferable to the original PDQ in terms of the unidimensional construct for people with chronic WAD. The Rasch item-person maps (see fig 1) demonstrated that the modified PDQ items difficulty levels appeared to encompass most people with chronic WAD, indicating a wellmatched targeting of the modified PDQ items to the chronic whiplash population. In addition, it supports the finding of lack of floor or ceiling effects. Unfortunately, the item gaps in the modified PDQ (particularly in the prospective memory section) remained evident. This could suggest that the modified PDQ could NDI be expanded in a more comprehensive way for people with chronic WAD. One possible way would be to add extra items to fill the gaps between the existing items, which could balance the deviation between mean item difficulty and person ability. Regarding the external construct validity, this research provides preliminary evidence that the modified PDQ has convergent validity to the NDI. However, this does not indicate that the NDI can be used instead of the modified PDQ because the NDI is not a specific measure for disability resulting from cognitive symptoms, although the NDI includes 1 cognitive dimension (concentration). In addition, there is a significant correlation between attention/concentration and organization/ planning abilities and self-reported neck pain intensity. This accords with the fact that concentration and attention, which could affect organization/planning abilities, are affected by pain, and individuals with WAD demonstrate difficulty in dividing and/or shifting attention The correlation between prospective memory and age also accords with the fact that prospective memory reduces with age. 37 There was no correlation between the retrospective memory section of the modified PDQ and age, which also accords with findings by Crawford et al. 38 Scores in the PDQ were significantly higher in the whiplash than the control group across all sections of both the modified and the original PDQ, which is consistent with the findings of Sullivan et al. 5 This indicates discriminate validity of both versions of the questionnaire. In test-retest reliability, item 15 from the prospective memory section, I forget to take my medication, demonstrated poor reliability in people with chronic WAD. However, the sectional scores demonstrated acceptable test-retest reliability. Therefore, test-retest reliability of the modified PDQ can be considered acceptable in this group. This study has demonstrated the validity and reliability of the modified PDQ to gain a basic understanding of the degree of perceived cognitive symptoms in people with chronic WAD. Future studies could use the modified PDQ with confidence to investigate further unexplored issues related to cognitive symptoms in this WAD group. For example, investigation of the external validity of the PDQ with other self-reported questionnaires or neuropsychologic tests is warranted. The investigation of other items to fill the gaps between existing items and the development of relevant cutoff scores for the PDQ or other clinical tests may enhance the assessment of cognitive symptoms in people with chronic WAD. Study Limitations This study used a sample of convenience without consideration of educational levels or specific clinical characteristics of the chronic WAD sample, which may limit the generalizability of results to other groups of chronic WAD. Table 5: Comparison of PDQ Scores Between Chronic WAD Group and Control Group Original Modified Group Attention/ Concentration (0 20) Retrospective Memory (0 20) Attention/ Concentration (0 16) Retrospective Memory (0 16) Prospective Memory (0 20) Organization/ Planning (0 20) Chronic WAD (n 105) Control (n 50) P* Cohen s d Values are mean SD or as otherwise noted. *Independent sample Mann-Whitney U test.

7 1780 COGNITIVE SYMPTOMS IN CHRONIC WHIPLASH DISORDERS, Takasaki Table 6: Test-Retest Reliability in Each Item and Total Scores in Each Section in the Original and Modified PDQ Items (Item Number and Description) Original PDQ ICC (95% CI) Modified PDQ Quadratic Weighted Attention/concentration.82 (.64.92).81 (.62.91) 1. I lose my train of thought when I am speaking During conversation, I have difficulty concentrating on what people are.70 saying. 3. I have trouble concentrating on things like watching a television program or reading a book I find that my mind tends to drift a lot I have trouble holding telephone numbers in my head, even for a few seconds.*.77 Retrospective memory.84 (.67.92).83 (.66.92) 6. I have difficulty remembering the names of people even if I have met them several times.* I can t remember if I have already done something I can t remember what I did the night before After a telephone conversation, I can t remember what we talked about I can t remember what I did last weekend..83 Prospective memory.82 (.64.92) NA 11. I forget what I came into the room for I miss appointments and meetings I ve scheduled I can t remember the date without looking it up I forget to do things like turn off the stove, or turn on my alarm clock I forget to take my medication..31 Organization/planning.79 (.59.90) NA 16. I have trouble getting things organized I have difficulty planning what to do during the day Even though I have a lot of things to do, I have a lot of trouble getting started At times, it seems like my mind goes totally blank I have trouble making decisions..80 Abbreviations: CI, confidence interval; ICC, intraclass correlation coefficient; NA, not applicable. *Excluded in the modified PDQ. NA because of no modification. CONCLUSIONS The modified PDQ appears a valid and reliable questionnaire to provide a basic understanding of the degree of perceived cognitive symptoms in people with chronic WAD. References 1. Radanov BP, Di Stefano G, Schnidrig A, Sturzenegger M. Common whiplash: psychosomatic or somatopsychic? J Neurol Neurosurg Psychiatry 1994;57: Radanov BP, Sturzenegger M, De Stefano G, Schnidrig A. Relationship between early somatic, radiologic, cognitive and psychosocial findings and outcome during a one-year follow-up in 117 patients suffering from common whiplash. Br J Rheumatol 1994; 33: Radanov BP, Sturzenegger M, Di Stefano G. Long-term outcome after whiplash injury: a 2-year follow-up considering features of injury mechanism and somatic, radiologic, and psychosocial findings. Medicine (Baltimore) 1995;74: Soderlund A, Lindberg P. Long-term functional and psychological problems in whiplash associated disorders. Int J Rehabil Res 1999;22: Sullivan MJ, Hall E, Bartolacci R, Sullivan ME, Adams H. Perceived cognitive deficits, emotional distress and disability following whiplash injury. Pain Res Manag 2002;7: Sturzenegger M, Radanov BP, Winter P, Simko M, Farra AD, Di Stefano G. MRI-based brain volumetry in chronic whiplash patients: no evidence for traumatic brain injury. Acta Neurol Scand 2008;117: Ling J, Campbell C, Heffernan TM, Greenough CG. Short-term prospective memory deficits in chronic back pain patients. Psychosom Med 2007;69: Edgley K, Sullivan MJL, Dehoux E. A survey of multiple sclerosis, Part 2: determination of employment status. Can J Rehabil 1991;4: Woods SP, Carey CL, Moran LM, Dawson MS, Letendre SL, Grant I. Frequency and predictors of self-reported prospective memory complaints in individuals infected with HIV. Arch Clin Neuropsychol 2007;22: Woods SP, Iudicello JE, Moran LM, et al. HIV-associated prospective memory impairment increases risk of dependence in everyday functioning. Neuropsychology 2008;22: Cuttler C, Graf P, Pawluski JL, Galea LAM. Everyday life memory deficits in pregnant women. Can J Exp Psychol 2011;65: Moller JT, Cluitmans P, Rasmussen LS, et al. Long-term postoperative cognitive dysfunction in the elderly: ISPOCD1 study. Lancet 1998;351: Sullivan MJ, Edgley K, Dehoux E. A survey of multiple sclerosis, Part 1: perceived cognitive problems and compensatory strategy use. Can J Rehabil 1990;4: Spitzer WO, Skovron ML, Salmi LR, et al. Scientific monograph of the Quebec Task Force on Whiplash-Associated Disorders: redefining whiplash and its management. Spine 1995; 20:1S Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther 1991;14:

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