When can a risk factor be used as a worthwhile screening test?

• Published in: BMJ 1999-12, Vol.319 (7224), p.1562-1565
• Main Authors: Wald, N J, Hackshaw, A K, Frost, C D
• Format: Article
• Language: English
• Subjects: Cardiovascular disease; Cholesterol; Disease risk; Disorders; Education and Debate; Epidemiology; False positive errors; False Positive Reactions; Health risk assessment; Heart; Humans; Lung cancer; Mass Screening - methods; Medical screening; Myocardial ischemia; Odds Ratio; Predisposing factors; Pregnancy; Risk Assessment; Risk Factors; Screening tests; Sensitivity and Specificity; Serum cholesterol; Spina bifida
• ISSN: 0959-8138; 1468-5833; 1756-1833
• DOI: 10.1136/bmj.319.7224.1562

Summary points To be a worthwhile screening test, a risk factor must be strongly associated with a disorder The strength of association between a risk factor and a disorder can be quantified by the relative risk or relative odds (odds ratio) A risk factor can also be considered as a screening test, and its association with the disorder can be quantified as the detection rate for a specified false positive rate There is a direct numerical equivalence between the relative odds and the detection rate for specified false positive rate that does not depend on the incidence or prevalence of the disorder A relative odds of 5 between the highest and lowest fifths of the distribution of a risk factor is equivalent to only a 14% detection rate for a 5% false positive rate if the SDs of the risk factor in people with and without the disorder are the same Expressing risk as a relative odds usually compares risk in the tails of the distribution of the risk factor; this can give an overoptimistic impression of the value of the risk factor used as a screening test Methods Relative risk and relative odds The strength of an association between a risk factor and a disorder can be quantified by a dose-response relation between the incidence of the disorder and increasing values of the risk factor. Methodological relation The two methods of quantifying the relation between a variable and a disorder (illustrated by figs 1 and 2 ) are directly related if the frequency distribution of the variable is Gaussian in both affected and unaffected individuals. [...]for any value of the ROQ1-5 there will be an equivalent DR5 and vice versa.