Table 2

Considerations for estimating the benefits and harms of a screening programme, modified from Harris, Sawaya, Mover and Calonge23

Magnitude of potential benefits
Probability of CVD event without screeningThe screening programme attempts to reduce and its probability in the proposed target population is needed to judge the benefit.
The proportion detected by screening of all in the target group who would suffer the adverse health outcomeThe purpose of screening is to detect those people who will experience the CVD event. Screening people positive who will not suffer the adverse CVD event is not a benefit (but overdiagnosing—see later).
Magnitude of incremental health benefit of screening caused (early) versus later clinical treatmentScreening must provide a better benefit than clinical detection to reduce morbidity or mortality. The incremental benefit must be estimated in absolute terms as convincing/impressing relative terms is possible without much absolute benefit.
Magnitude of potential harms
Cumulated proportion of false-positive screening testsAs many screening programmes perform repeated screening after a time period, the best estimate of false-positive screening tests is consequently the cumulative percentage of people screened who have at least one false-positive screening test over a period of time, such as 10 years.
Experience of people with false-positive resultsA negative experience may come from either physical (discomfort or complications from further testing) or psychological (anxiety, depressive symptoms, reduced Qol).
Small or infrequent negative experiences but experienced by many may cumulate to large harms for a population.
Proportion of overdiagnosisDoes earlier diagnosis (due to screening) compared with later diagnosis (due to clinical detection) cause increased diagnostic evaluation (with discomfort) or treatment (with discomfort and complications)?
Experience of people who are overdiagnosedThe absolute severity of the adverse health effect due to increased detection by screening, diagnostic evaluation or treatment resulting from earlier diagnosis is important to estimate.
Proportion and severity of harms of work-up and treatment of true positivesFor people found to have conditions that would lead to the adverse health outcome, harms from earlier work-up or treatment means they will suffer these harms for a longer time, thus reducing net benefits.
  • CVD, cardiovascular disease; Qol, quality of life.