A 31-year-old woman brings her 18-month-old son to the pediatrician for a well-baby checkup. She is extremely concerned that her child has been gaining weight at an accelerated pace. She asks how her son's risk of developing childhood obesity before his early school-age years compares with that of children who gain weight at a normal pace. Which of the following types of study designs would best answer her question?
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Observational studies are broadly classified as having a descriptive or analytic design.
Descriptive designs (eg, case report, case series, cross-sectional) describe patterns of disease in populations by time, place, and person. These studies help generate hypotheses about associations between risk factors and disease, such as in a study showing that a high proportion of people with lung cancer are also smokers.
Analytical designs (eg, case-control, cohort, some cross-sectional designs) test hypotheses about associations between risk factors and disease, such as in a study that determines that smoking is a statistically significant risk factor for lung cancer.
The choice of study design to address a specific research question is guided by a study's objective, the disease of interest, its apparent association to risk factors, and feasibility constraints.
In this question, the mother of an 18-month-old child who seems to be gaining weight at an accelerated pace is concerned about her child's risk of developing childhood obesity compared with that of children who gain weight at a normal pace. This suggests that the mother identifies the accelerated weight gain in young children as a potential risk factor for childhood obesity. To answer the mother's question, the study design would have to test a hypothesis about the association between a risk factor (eg, accelerated weight gain in young children) and disease (eg, childhood obesity). Therefore, the study must have an analytical design (Choices B and C). The analytical study design that compares the risk of developing disease (eg, childhood obesity) between exposed (eg, young children with accelerated weight gain) and nonexposed (eg, young children with normal weight gain) groups is the cohort study.
(Choice A) A case-control study is an analytical design in which potential participants are initially identified based on disease status as cases (ie, with disease) or controls (ie, without disease). Once cases and controls are identified, the presence of past exposure to ≥1 risk factors of interest is determined in each group. Because cases, by definition, already have the disease, case-control studies cannot calculate and compare risk of developing disease.
(Choice E) A cross-sectional study takes a snapshot of a population to estimate the prevalence of risk factors and disease simultaneously, so this study design cannot calculate and compare risk of developing disease.
Educational objective:
A cohort study is an analytical study design that estimates and compares the risk of developing disease between exposed and nonexposed groups.