prevalence and incidence of a wide variety of disorders and illnesses. Morris (1964),
in his book Uses of Epidemiology, stressed the importance of penetrating to the
‘early minor stages’, then back to the precursors of disease and then back to its pre-
dispositions. In 1968, Butterfield, in a Rock Carling Lecture on priorities in medicine,
advocated a new emphasis on screening in health-care delivery. This enthusiasm
is reflected in a statement by Edward VII that is often repeated: ‘If preventable, why
not prevented?’GUIDELINES FOR SCREENING
As a result of the enthusiasm for screening, sets of criteria have been established. Wilson
(1965) outlined the following set of screening criteria: The disease
An important problem
Recognizable at the latent or early symptomatic stage
Natural history must be understood (including development from latent to
symptomatic stage)
The screen
Suitable test or examination (of reasonable sensitivity and specificity)
Test should be acceptable by the population being screened
Screening must be a continuous process
Follow-up
Facilities must exist for assessment and treatment
Accepted form of effective treatment
Agreed policy on whom to treat
Economy
Cost must be economically balanced in relation to possible expenditure on medical
care as a whole.
More recently, the criteria have been developed as follows: The disease must be sufficiently prevalent and/or sufficiently serious to make early
detection appropriate.
The disease must be sufficiently well defined to permit accurate diagnosis.
There must be a possibility (or probability) that the disease exists undiagnosed in
many cases (i.e. that the disease is not so manifest by symptoms as to make rapid
diagnosis almost inevitable).
There must be a beneficial outcome from early diagnosis in terms of disease treat-
ment or prevention of complications.
There must be a screening test that has good sensitivity and specificity and a
reasonably positive predictive value in the population to be screened.214 HEALTH PSYCHOLOGY