642 Obstetrics and Gynecology Board Review •••
❍ What biases are present in the screening process?
The three types of bias present in the screening process are volunteer (selection) bias, lead-time bias, and length-
time bias. Volunteer bias refers to the fact that volunteers tend to be better educated and in better health than the
general population. Lead-time bias refers to the increased survival duration introduced by early recognition of the
disease (lead-time) through the screening process. Length-time bias refers to the fact that screening preferentially
identifies more slowly progressing diseases that tend to have a better prognosis.
❍ How are patterns of disease occurrence characterized in epidemiology studies?
Patterns of disease are characterized by person, place, and time.
❍ What study designs are used for descriptive epidemiology studies?
Correlational studies, case-reports or case-series, surveys, and surveillance studies. The results of descriptive
epidemiology studies can form hypotheses for analytic research.
❍ What are correlational studies?
Correlational studies are used to identify associations between risk or causative factors and disease. They cannot
determine causation.
❍ What are case-reports or case-series?
A case-report is a unique experience of one patient. A case-series is a small group of patients with a similar
diagnosis.
❍ What are survey studies?
Survey studies provide an overview of people studied at one point in time for a wide variety of descriptive
information. Survey data cannot answer questions about disease etiology.
❍ What is disease surveillance?
Disease surveillance refers to a systematic method for monitoring patterns of disease occurrence and health
outcomes in a population.
❍ What is SEER?
SEER is an acronym for Surveillance, Epidemiology, and End Results program. It is a population-based registry
utilized and managed by the U.S. National Cancer Institute as one way of monitoring the incidence of cancer by
geographic area.
❍ Define analytic epidemiology.
Analytic epidemiology attempts to explain possible causes for the occurrence of a disease.
❍ Analytic epidemiology must first establish if an association exists between a specific factor and the disease in
question. What are measures of association?
Relative risk (RR), odds ratio (OR), attributable risk (AR), and population attributable risk (PAR) are all measures
of association.