Epidemiology for Canadian Students: Principles, Methods and Critical Appraisal by Scott Patten

Author:Scott Patten [Patten, Scott]
Language: eng
Format: azw3
Publisher: Brush Education
Published: 2015-03-17T04:00:00+00:00

Assessing associations in a prospective cohort study using ratio-based measures

Prospective cohort studies exclude cases of disease at a baseline point in time, which makes it possible to assess risk for disease in both the exposed and nonexposed groups.

The parameter that quantifies risk may be a risk ratio (incidence proportion ratio), incidence rate ratio, or a hazard ratio.

RISK RATIOS

Where the incidence proportion is concerned, this leads to the familiar 2 × 2 contingency table of exposure versus disease presented in Table 29. Note, however, that this table only looks familiar: it is very different from a contingency table for a cross-sectional or case-control study. In a prospective cohort study, it includes only study subjects at risk of the disease at baseline. The classification of these subjects as having or not having disease depends on whether they develop the disease during the period of observation of the study. This differs from studies that focus on a point in time (cross-sectional studies) and studies that select participants based on disease status (case- control studies).

Key point: The 2 × 2 contingency table for a prospective cohort study looks similar to that of other types of study, but its meaning is different.

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