In this study on the validity of self-reported diabetes in a large Kurdish population, we found self-reported diabetes had a moderate sensitivity of 78.5%, a high specificity of 93.9%, a fairly good positive predictive value for self-reporting diabetes of 58.7%, and a high negative predictive value for self-reporting no diabetes of 98.0%. The agreement between self-reported diabetes and reference criteria was fairly good with Kappa of 65.1% and concordance of 92.3%. Besides, we showed that the demographic, anthropometric, and habitual features of subjects had largely influenced the accuracy of self-reported diabetes. In this case, being female, increase in age, increase in BMI, being an ex-smoker, having HTN, and family history of diabetes increase the odds of true positive rate in diabetes self-reports. We found 31% of diabetic participants (120 out of a total of 386) were not under any medication for diabetes. The previous reports on this issue showed almost the same statistics [15, 16]; however, we demonstrated an updated validation of diabetes self-reports among a large Kurdish population of Iran.
The epidemiological surveys commonly applied either self-report or medical records of chronic diseases to estimate their incidence or prevalence . Among chronic diseases, self-reports of diabetes were identified to be more accurate with a higher level of agreement [18–20]. Our findings on the accuracy of self-reported diabetes were in line with the recent similar studies that showed the sensitivity of 75-79.3% and specificity of 95.8-98.4% [16, 21]. However, older previous studies showed lower sensitivity of 61.5-69.7% for diabetes self-reports [20, 22]. This increasing trend in the accuracy of diabetes self-reports can be explained by the increase in awareness of society and the development of the health care system over time . Meanwhile, the difference in this accuracy over time can be due to the different demographic features of the studied population since we similar to previous studies revealed that the accuracy of diabetes self-reports was largely dependent on the baseline characteristics of study participants [4, 16, 20].
The results of the multivariable analysis showed that women were more likely to have a disagreement of self-reported diabetes with the reference, higher false positive and true positive rates and lower false negative rate than men. One explanation for this finding is that women take better self-care behaviors and use more health care services . Moreover, women take more attention to their dietary consumption. In this instance, they tend to count daily carbohydrates intake and consume less fat . Thus, they were more likely to find themselves in diabetic condition and reported more true positives and false positives. We also found that increment in the age of study participants was associated with higher odds of true positive and false negative rates of self-reported diabetes. The higher false negative self-reports in older participants can be due to a recall bias because of Alzheimer's disease or age-related memory loss  and higher true positive self-reports among older individuals can be due to more health care delivery and more opportunity to undergo blood sugar testing in this population . We also observed that increment in BMI was associated with higher odds of the discordance between diabetes self-reports and the reference criteria, higher true positives, false negatives, and false positives of self-reported diabetes. In the previous studies in line with this study, obesity, as well as an increase in BMI, resulted in higher odds of diabetes development in this population and consequently higher true positive and false negative rates [16, 20, 27]. This finding can be attributed to insulin resistance condition in obesity as well as poor self-care of overweight and obese individuals [28, 29].
In this study, participants with HTN were more likely to truly report their diabetes. This finding can be due to better monitoring of other metabolic syndrome risk factors in this population and higher awareness about their health. In line with previous studies, we observed no significant change in the odds of false negative and false positive rates among populations with HTN .
Positive family history of diabetes, particularly from the first-degree relatives, showed a high level of discordance in diabetes self-reports. In this instance, subjects with positive family history were more likely to develop diabetes that this issue explained higher true positive rates of diabetes self-reports in this group. Besides, similar to previous studies, subjects with positive family history tend to report diabetes more frequently which leads to higher false positive rates [16, 30].