Step 2. Characterizing the Limitations of Health Data

• Epidemiologic Studies

The ability of an epidemiologic study to detect an increased incidence of disease is dependent on the increased risk level and on the size of the affected population. For example, if an estimated exposure results in an increased cancer incidence of 1 in 10,000 over background (a high risk level), it would not be detectable in a study population of several thousand people (a very large cohort.)

Additional epidemiologic study limitations might include

• exposure variability over time (past and present) and populations
• latency periods between exposure and health outcome (cancer, for example)
• confounding factors (such as smoking or alcohol use)
• different measurement points for exposure (for example, average or lifetime)
• incomplete or inaccurate monitoring systems
• small study size
• people moving into and out of the study area

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