Obtaining valid information

Validity in respect of information that is collected in an epidemiological study is a measure of how accurate the data collected are, relative to an underlying truth. Classical approaches aim to ensure that the approach is both sensitive (low false negatives) and specific (low false positives) as, for example, in determining the presence or absence of a disease. A modified approach is needed where the value of an attribute is collected. Underpinning both these approaches is the need to consider what is the test of the underlying truth. The reader may already be aware of the application of validity tests in assessing the performance of diagnostic and screening tests. It is conventional to evaluate this performance in terms of the two indicators, sensitivity and specificity.