Methods of investigation in clinical cardiology. X. Studies on the evaluation of diagnostic tests in cardiology

Diagnosis is a complex cognitive process which is characterised by uncertainty. This uncertainty can be managed through specific knowledge in conjunction with probability theory. Studies evaluating diagnostic tests are the best way of building this knowledge. Studies evaluating diagnostic tests have two essential components: the gold standard and the new test. Both components, gold standard and test, are independent measurement process that can be influenced by diverse sources of variability. The comparison between diagnostic and test is essentially a hierarchical procedure. Diagnostic tests are evaluated by their sensitivity, specificity compared to a definitive gold standard. The predictive values and the likelihood ratio test are also used. Sensitivity (the proportion of true positives) and specificity (the proportion of true negatives) are values obtained from a sample and thereby can be considered as the conditional agreement between gold standard and the new test. Kappa coefficients for sensitivity and specificity are useful tools for adjusting both indices. Sensitivity and specificity are non-poblational values, they are estimates of the true values of the study population and can be affected by random error and systematic errors (bias). Confidence intervals are useful for giving an indication of the precision of the point estimates of sensitivity and specificity. A suitable sound design is required to avoiding a biased estimate of sensitivity, likelihood ratio, and predictive values. Finally a list of potential biases is given with methods for minimising these.