(Stroke. 2001;32:2232.)
© 2001 American Heart Association, Inc.
Original Contributions |
From the Roudebush Veterans Administration Medical Center, Department of Neurology, Indiana University School of Medicine, Regenstrief Institute for Health Care, Indianapolis (W.J.J., L.S.W.), and Department of Neurology, Mayo Clinic, Jacksonville, Fla (J.F.M.).
Correspondence to William J. Jones, MD, Regenstrief Institute, 1050 Wishard Blvd, RG-6, Indianapolis, IN 46202. E-mail wjjones{at}IUPUI.edu
| Abstract |
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Methods A research assistant administered the QVSFS to outpatients from Veterans Administration stroke and general medicine clinics. Subjects were defined as QVSFS negative if responses to all 8 questions were negative. Questions requiring rephrasing or clarification were noted. Neurologists, blinded to QVSFS scores, interviewed and examined all subjects to determine stroke-free status, defined as no history or examination findings of previous stroke and/or TIA.
Results One hundred fifty-five subjects were examined; mean age was 70 years; 98.1% were male. Seventy-eight subjects were determined to be stroke free by the neurologist. The negative predictive value of the QVSFS was 0.96, with positive predictive value of 0.71. No question required rephrasing or clarification >5 times. Twenty-two subjects (14.2%) required rephrasing or clarification of at least 1 question.
Conclusions The QVSFS can effectively identify stroke-free individuals with a high degree of accuracy, even in a population with a large proportion of patients with prior stroke or TIA. Accuracy for identifying subjects with stroke and/or TIA is lower, but the QVSFS may still be useful as a screening tool in that regard.
Key Words: cerebral ischemia, transient stroke stroke assessment
| Introduction |
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| Subjects and Methods |
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The research assistant approached patients in the clinic, explained the study, and obtained informed consent. The research assistant administered the QVSFS (Figure) to those patients who consented and also recorded demographic information, including age, sex, and educational level. During the same clinic visit, a neurologist blinded to the QVSFS results interviewed each patient and performed a neurological examination. Both the research assistant and study neurologist were unaware of the stroke status of participants at the time patients were offered enrollment in the study. Study subjects were not told the results of either the QVSFS or the neurologists determination of their stroke status.
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QVSFS scores range from 0 (no questions positive) to 8 (all 8 questions positive). Subjects were considered QVSFS negative (stroke/TIA free) if their sum score was 0. If any of the 8 items were positive (sum score 1 to 8), the QVSFS was considered positive (not stroke/TIA free.) Any question that was answered "unknown" was scored as a negative response. The alternative approach, scoring all "unknown" responses as positive, would have changed the QVSFS outcome in 6 subjects. The research assistant prospectively recorded every time a question had to be rephrased or clarified for the patient. If the neurologist determined that the examination was abnormal, the neurologist stated whether the abnormality was due to stroke or due to another cause. The examining neurologist determined each subjects stroke status (stroke, TIA, or neither) on the basis of the face-to-face interview and examination results. This determination, based on history and examination, was considered the benchmark for stroke status in this study.
Test characteristics of the QVSFS were compared with benchmark determination of stroke status by Fishers exact test. Subject characteristics were compared with Fishers exact test or t tests between stroke-free subjects and subjects who were not stroke free. Comparisons were done separately for stroke status defined by the QVSFS and for stroke status determined by the benchmark history and examination. Age and educational level of subjects were also compared with t tests between those who did and those who did not require rephrasing or clarification of items. Positive and negative likelihood ratios were calculated to assess the relationship of each item and the QVSFS overall to the benchmark stroke status determination. The study was approved by the local human subjects review board.
| Results |
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Seventy-seven (49.7%) of the 155 subjects were found to have stroke/TIA as determined by the benchmark (Table 2). Of these 77, the QVSFS was also positive in 75 (97.4%; P<0.0001). In the 78 subjects who were stroke/TIA free by the benchmark, the QVSFS was negative in 47 (60.4%). The overall sensitivity and specificity for the QVSFS were 0.97 (95% CI, 0.94 to 1.0) and 0.60 (95% CI, 0.49 to 0.71), respectively. The NPV (ie, the probability of correctly identifying a stroke/TIA-free patient) was 0.96 (95% CI, 0.90 to 1.0), and the PPV (ie, the probability of correctly identifying a patient with stroke/TIA) was 0.71 (95% CI, 0.62 to 0.79). The positive and negative likelihood ratios were 2.45 and 0.04, respectively. The positive likelihood ratio is the odds of a positive QVSFS result in an individual with stroke/TIA (sensitivity/1-specificity); the negative likelihood ratio is the odds of a negative QVSFS result in an individual with stroke/TIA (1-sensitivity/specificity).
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All of the 6 subjects whose QVSFS status would have changed if "unknown" responses had been scored positive were stroke/TIA free by the benchmark (ie, false-positive by QVSFS). This would result in no change in the sensitivity. The NPV would decrease only slightly from 0.96 to 0.95, and the negative likelihood ratio would slightly increase from 0.04 to 0.05. Specificity and PPV would decrease from 0.60 to 0.53 and from 0.71 to 0.67, respectively, and the positive likelihood ratio would decrease from 2.45 to 2.05.
The proportion of subjects answering "no" to each of the 8 questions ranged from 60.0% for question 1 to 85.2% for question 6 (Table 3). None of the individual items performed as well as the overall QVSFS. The sensitivity of the individual items ranged from 0.22 to 0.79, while the specificity ranged from 0.78 to 0.99. Question 1 was the most sensitive (0.79) and specific (0.99) individual item. The least sensitive were questions 6 and 7 at 0.22, with specificity of 0.92 and 0.87, respectively. The least specific individual item was question 4 at 0.78 (sensitivity, 0.56). The PPV for the individual questions ranged from 0.63 to 0.98. Only questions 5 and 7 had lower PPV (0.66 and 0.63, respectively) than the QVSFS as a whole. Accordingly, the positive likelihood ratios for questions 5 (1.94) and 7 (1.72) were also lower than the overall QVSFS, while for the other 6 questions the positive likelihood ratio was higher (2.56 to 61.79). The NPVs for the individual items ranged from 0.53 to 0.83, while the negative likelihood ratios ranged from 0.21 to 0.89.
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Twenty-two study participants (14.2%) needed
1 of the questions to be rephrased or clarified (Table 3.) Only 3 of the 22 needed >1 question to be rephrased or clarified. All of the questions required rephrasing or clarification at least once. Question 1 required rephrasing or clarification the most at 5 times, while question 7 was least likely to require rephrasing or clarification (once). The average educational level of the subjects requiring rephrasing or clarification was 11±3 years (versus 12±3 years for those not needing rephrasing or clarification; P=0.09.) The average age of the subjects requiring rephrasing or clarification was 68±8 years (versus 70±8 years for those not needing rephrasing or clarification; P=0.21.) Half (11/22) of the questions requiring rephrasing were answered positive after rephrasing. Ten of the 20 subjects requiring
1 question to be rephrased or clarified were determined to have stroke on the basis of the benchmark (none were determined to have had a TIA). Of the 5 subjects requiring rephrasing or clarifying of question 1, 3 needed stroke to be distinguished from a heart attack, 1 reported a "sun stroke," and 1 reported a seizure. All 4 of those requiring rephrasing or clarification of question 2 needed to have TIA defined for them. Six participants required emphasis of "sudden" onset of symptoms (questions 3, 4, 5, 7, and 8). Along with needing the term sudden emphasized twice for question 5, cataracts, eye injury, and nonspecific, transient descriptions of visual disturbances accounted for all of the confusion regarding questions 5 and 6.
| Discussion |
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Another important aspect of validity is questionnaire and item comprehension in the intended population. We found that the QVSFS was easily understood by most subjects. Fewer than 1 in 7 of the participants needed to have
1 question rephrased or clarified, and fewer than 1 in 56 questions needed rephrasing or clarification. The average educational level of subjects requiring rephrasing or clarification was approximately 1 year less than that in those not requiring rephrasing or clarification, a difference that approached statistical significance. However, there was no significant difference in the age of those needing rephrasing or clarification. Collectively, mistaken understanding of stroke or TIA was the most common reason for needing rephrasing or clarification and accounted for nearly half (9 of 22; all 5 of question 1 and all 4 of question 2) of the questions requiring rephrasing or clarification. Emphasis on sudden onset of symptoms accounted for 6 questions requiring clarification. Five questions required rephrasing or clarification because of other ocular diseases or symptoms not related to stroke/TIA. Importantly, this level of comprehension was observed in a population of clinic patients rather than in a group of hospital volunteers who are likely to be healthier and less likely to have multiple symptoms than subjects recruited from the clinic.
Previous studies have used either a single question about prior stroke812 or a multiple-item questionnaire about previous stroke and stroke symptoms to identify stroke cases.1318 Most of these studies did not report test characteristics such as sensitivity or specificity.8,10,11,13,14,1618 In the reports that did, sensitivity and specificity were 69% and 98%, respectively, for one instrument and 81.8% and 85.7%, respectively, for the other instrument.9,15 One study did not report sensitivity or specificity but did report the true-positive rate as 67%.12 Berger and colleagues19 compared a single question with a multiple-item questionnaire of stroke symptoms and found, as we did, increased accuracy using the multiple-item questionnaire versus a single question about previous physician-diagnosed stroke to assess stroke status in a general population. The sensitivity of their complete questionnaire was 89.5%. They also suggested different methodological strategies depending on the purpose for which an instrument is being used: prevalence or incidence estimation, risk factor analysis, or selection of proper controls.
The purpose of the QVSFS, to identify individuals who are free of stroke/TIA, is most consistent with the strategy of selecting proper controls suggested by Berger et al.19 For this strategy they used 2 questions about impairment of vision and a question about previously diagnosed stroke, which resulted in a sensitivity of 84.2%, moderately lower than the overall sensitivity of 97% for the QVSFS. Another potential use of the QVSFS, given the low negative likelihood ratio of 0.04, is to assist in case ascertainment of subjects with stroke by efficiently reducing the number of subjects requiring a comprehensive medical record review and/or examination. Since fewer than 1 in 25 subjects with stroke/TIA would be labeled stroke/TIA free by the QVSFS, this may reduce the time and cost of accurately identifying stroke cases.
Although the QVSFS was accurate for identifying stroke/TIA-free patients in this study, some limitations remain. Recall bias and comorbidity may both reduce the sensitivity and specificity of a questionnaire if symptoms are incorrectly ascribed to stroke. To limit this potential bias in our cohort of chronically ill patients, we validated our results by physician history and examination, which most accurately classifies stroke/TIA status, and found that the sensitivity of the QVSFS remained very high. In addition, the performance characteristics of the QVSFS are not yet established for self-administration (for example, by postal survey). Additionally, the subjects in this study were predominantly men, although the original QVSFS validation sample included a more representative proportion of women and found very similar results. In addition, while valid for the purpose of identifying stroke/TIA-free individuals, the QVSFS may misclassify some individuals as having stroke/TIA when they are actually stroke/TIA free. The resulting implication for investigators is that, if they use the QVSFS to identify individuals with stroke, the presence of stroke must be confirmed by another means.
Accurate identification of stroke status is fundamental to many types of stroke research. The QVSFS provides a rapid, valid means of identifying stroke/TIA-free subjects. It may also be used to reduce the number of potential subjects screened with more labor-intensive methods for the purpose of case ascertainment. Work in SWISS will help to further confirm the generalizability across a heterogeneous sample and to establish the reliability of the QVSFS.
| Acknowledgments |
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Received March 7, 2001; revision received June 1, 2001; accepted June 28, 2001.
| References |
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