Skip to Main Content

The Lentis study is designed to evaluate a new treatment for infantile eczema. Infants with eczema are recruited for the study. After families are recruited and consented, the infants are randomly assigned to receive either the treatment cream or a placebo cream. Parents are instructed to give the assigned cream 3 times a day for the next 10 days. After 10 days, the investigators will reexamine the study patients. The treatment cream and the placebo cream are both identical in terms of appearance, smell, and texture. The Lentis study uses what type of study design?

A. Case-control study

B. Cohort study

C. Observational study

D. Randomized controlled trial (RCT)

E. Quasi-experimental study

Answer: D

RCTs are usually the best study designs to answer questions about therapy. In an RCT, after recruitment and consent, the study participants are randomly assigned either to an intervention group or to a comparison group. In the Lentis study, the comparison was a placebo cream. Randomization helps decrease the likelihood of bias in assigning the study participant to a particular group. The study then compares the 2 groups as they move forward in time simultaneously.

In a case-control study, participants are recruited on the basis of an outcome (eg, severe eczema or mild eczema). The investigators then look backward in time to assess for an exposure of interest (eg, daily bathing vs infrequent bathing as an infant). If daily bathing is hypothesized to be associated with severe eczema, then there would be a higher percentage of infants with severe eczema who had a history of daily bathing (compared to infants with mild eczema). The case-control design is useful for evaluating claims of causation.

In a cohort study, participants are recruited on the basis of an exposure (eg, infants who live near freeways vs infants who do not live near freeways). In the cohort study design, the investigators follow a group of participants from a point in time to another point in time to assess if an outcome of interest occurs. The cohort design is useful for studying the effects of rare exposures or for studying the prognosis of a condition.

The term observational study is descriptive, but not specific. An observational study can refer to a cohort study, case-control study, cross-sectional study, or even a case series or case study (Figure 2-1). Unlike an interventional study, an observational study usually takes advantage of a “natural” experiment.

A quasi-experimental study usually refers to the before and after evaluation of an intervention without the benefit ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.