Question

Prevalence-incidence bias occurs:

a.The exposure is associated with a decrease in both the incidence and prevalence of disease

b.Most commonly in cross-sectional studies

c.The outcome has an influence on the duration of disease

d.The disease has long duration

Answer 1

Answer is D: Prevalence-incidence bias is also known as Neyman's bias and is a Selection bias. The bias is mostly encountered with diseases under study having long duration than those with shorter ones. Also, Case-control studies are most susceptible to prevalence-incidence bias. However, the bias can occur in cross-sectional studies and cohort studies.

This occurs due to the long time interval between exposure and investigation. Late investigation of early exposed people leads to missing cases with fatal episodes. At the same time silent cases or cases with mild disease are also missed. A disease with long duration may have cases or patients with variable degree of illness. Some may die due to the disease and some may recover. At the same time, people affected or having exposure to the disease present with varying degree of severity. If patients who have died are excluded from the study, Disease appears less severe though there are large number of affected people at different interval of time. Similarly if patients who have recovered are left, the disease will appear more fatal. The best possible way to avoid this is to minimize the time interval between exposure and investigation.