Validity of self-reported prevalent cases of stroke and acute myocardial infarction in the Spanish cohort of the EPIC study

Siamak Sabour, Assistant Professor clinical epidemiology, MD, PhD,
May 22, 2012

The aim of the authors was to assess the validity and agreement of self-reported prevalent cases of stroke and AMI in the Spanish cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). They calculated sensitivity, specificity, positive predictive values and ? statistics. The sensitivity of self-reported prevalent cases of stroke was 81.3% and that for AMI was 97.7%. The positive predictive value was 22.2% and 60.7% for stroke and AMI, respectively. The agreement between self- report questionnaire results and medical records was substantial (?=0.75) for AMI but not for stroke (?=0.35).1 To scientifically assess the accuracy (validity) of a test, there are 7 estimations named Sensitivity, Specificity, Positive Predictive Value (PPV), Negative Predictive Value (NPV), Likelihood ratio positive, LR+ (true positive/false positive), Likelihood ratio negative, LR- (false negative/true negative) and finally Odds ratio, OR (true results /false results).2 Considering limitations of the first 4 estimations, preferably the last 3 estimations are being reported. However, due to the different range of these estimations [(LR+ from 1 to infinity; the higher, the better) (LR- from 0 to 1; the closer to the zero, the better) and OR greater than 50 indicates a valid test), usually two different tests are being evaluated compared to a gold standard. 2 Regarding agreement, to compute kappa value, just concordant cells are being considered, whereas discordant cells should also be taking into account in order to reach a correct estimation of agreement (Weighted kappa).2-4 It is crucial to know that there is no value of kappa that can be regarded universally as indication good agreement. Statistics cannot provide a simple substitute for clinical judgment. Two important weaknesses of k value to assess agreement of a qualitative variable are as follow: It depends upon the prevalence in each category and also depends upon the number of categories. So it is obvious that the less our categories, the higher will be our kappa value which can easily lead to misinterpretation.2-4

S.Sabour, MD, PhD

References: 1- Mach?n M, Arriola L, Larra?aga N, Amiano P, Moreno-Iribas C, Agudo A, Ardanaz E, Barricarte A, Buckland G, Chirlaque MD, Gavrila D, Huerta JM, Mart?nez C, Molina E, Navarro C, Quiros JR, Rodr?guez L, Sanchez MJ, Gonz?lez CA, Dorronsoro M. Validity of self-reported prevalent cases of stroke and acute myocardial infarction in the Spanish cohort of the EPIC study. J Epidemiol Community Health. 2012 May 10

2- Epidemiology, biostatistics and preventive medicine, Jeckel, 1st edition, 2008 3- Modern Epidemiology, K. Rothman, 3 rd edition, 2010 4- Clinical Epidemiology, D.E Grobbee, 1st edition, 2010

Conflict of Interest:

None declared

Conflict of Interest

None declared