Siamak Sabour
Diagnostic researches are among interesting field of clinical researches. However, methodological and statistical issues in such researches are not being considered appropriately. Diagnostic value should be considered as diagnostic accuracy (validity) and diagnostic precision (reliability or agreement). In case of binary variable, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio positive (LR+), likelihood ratio negative (LR-) as well as odds ratio (ratio of true to false results) are the most appropriate estimates to evaluate validity of a test compared to a gold standard. Therefore, it is better to report all these validity estimates together. Otherwise, final interpretation will be confusing. Moreover, it is important to know that for clinical purposes, reporting diagnostic added value should be considered using receiver operating characteristic (ROC) curve because all the above mentioned validity estimates can be acceptable while diagnostic added value may be clinically negligible. Regarding quantitative variables, Interclass correlation coefficient (Pearson r or spearman rho) can be considered as an appropriate statistical test to assess validity.