Weighing the evidence for and against a screening intervention is a complex task for policy makers and is likely to prove challenging for individual consumers too. In its latest edition, the US Preventive Services Taskforce has rated screening interventions on a five point scale, based on an assessment of whether benefits outweigh harms (or vice versa) and on the extent to which evidence is available to make that assessment.7
Unfortunately, the evidence available is often insufficient to make a recommendation.7
Even when evidence is available, policy makers have to judge whether the benefits outweigh the harms, and this decision is at least partly driven by the values of the people making the policy or recommendation. Their values may not accord with those of the individuals who are subsequently offered the screening test, underscoring the need for evidence based information to be presented to consumers.
To further complicate decision making, screening is implemented in various ways in different countries, on the basis of variable evidence, and with variable government regulation and protection for consumers. For example, evidence from randomised trials supports blood pressure screening,7
yet improved blood pressure screening and management through computerised systems is variably implemented.8
In contrast, cervical cancer screening programmes have been established within carefully regulated systems in many countries without evidence from randomised trials.7
Health authorities may also hold opposing views on whether screening is worthwhile—as, for example, in regard to prostate cancer.7,9
Finally, some screening (for example, by total body computed tomography) is available (and heavily marketed), even though there is no evidence that benefit outweighs harm, no endorsement from any health authority, and little regulation or protection for consumers.6
People need good information on the possible benefits and harms of screening
Thus we believe decision aids for consumers are urgently needed (and will be developed) on the substantial number of screening interventions now available. Below, we use examples from a range of screening programmes to illustrate the issues relating to development and use of decision aids (box).