The aim of a prospective cohort study conducted in a group of adults with diagnosed type 2 diabetes mellitus (T2DM) is to investigate the association between the presence of morbid obesity (BMI 40 kg/m²) and the risk of developing diabetic nephropathy. One of the groups in the study consists of adults with T2DM, a BMI 40 kg/m², and no diabetic nephropathy. Which of the following is the most appropriate comparison group for this prospective cohort study?

Question

The aim of a prospective cohort study conducted in a group of adults with diagnosed type 2 diabetes mellitus (T2DM) is to investigate the association between the presence of morbid obesity (BMI >40 kg/m²) and the risk of developing diabetic nephropathy. One of the groups in the study consists of adults with T2DM, a BMI >40 kg/m², and no diabetic nephropathy. Which of the following is the most appropriate comparison group for this prospective cohort study?

Quizplus · Accepted Answer

11ec160b_3730_3485_9249_7b96dea565ad_MD0001_00 A cohort study is an observational design in which potential participants in the population of interest are initially identified as exposed or nonexposed according to the independent variable (ie, exposure status to a risk factor). Once participants are categorized based on their exposure status, the occurrence (ie, incidence) of the dependent variable (eg, outcome of interest) over a specific period is determined in each group. Finally, the occurrence of the outcome is compared between exposed and nonexposed groups to estimate the association between the risk factors and the outcomes. If there is a statistically significant difference in outcome occurrence between the 2 groups, it is likely that the risk factor in question is associated with disease development. In this example: The population of interest is patients with type 2 diabetes mellitus (T2DM). Therefore, both the exposed and nonexposed groups must consist of patients with T2DM (Choices D and E). The risk factor of interest is morbid obesity (BMI >40 kg/m²). Therefore, the exposed group is adults with morbid obesity, and the nonexposed group is adults with normal weight (BMI 18.5 to <25 kg/m²) (Choice A). The outcome of interest is diabetic nephropathy. Exposed and nonexposed subjects must be selected with no history of the outcome because the occurrence of the outcome is what is measured during the study period (Choice B). Therefore, the exposed group is adults with T2DM who have morbid obesity and no diabetic nephropathy; the nonexposed group is adults with T2DM who have normal weight (BMI 18.5 to <25 kg/m²) and no diabetic nephropathy. Comparing the frequency of the outcome (eg, diabetic nephropathy) between exposed and nonexposed groups is what determines whether exposure to the risk factor (eg, morbid obesity) is associated with the risk of developing the outcome (eg, diabetic nephropathy). Educational objective: In a cohort study, subjects should be initially selected from the population of interest (eg, T2DM) based on their exposure status to a risk factor (eg, presence or absence of morbid obesity). Subjects are then monitored during the study period for development of the outcome of interest (eg, diabetic nephropathy). __________ References: Methodology series module 1: cohort studies. (http://www.ncbi.nlm.nih.gov/pubmed/26955090)

The Aim of a Prospective Cohort Study Conducted in a Group