Cluster Randomization Trials

6. Unit of Inference

Exercise 3

The goal of this exercise is to list of series of trial examples in which the user must determine whether the primary unit of inference is individual or cluster.

Read each example below and determine the primary unit of inference. Drag and drop the primary unit of reference into the appropriate example.

Units of Inference:
Individual
Cluster

The purpose of the study is to evaluate the effectiveness of different guideline implementation strategies in primary dental care. Participating dental practices were randomized to receive one of four different clinical guidelines related to the management of impacted teeth. The primary outcome was the proportion of patients in a practice whose treatment complied with the guideline.

The purpose of the study is to evaluate the effectiveness of a cholesterol screening program intended to lower the risk of cardiovascular mortality in a trial randomizing family practices to either the intervention strategy or a control. The influence of a patient’s level of education on the success of the intervention is also of interest.

Investigators wish to evaluate the effectiveness of treated nasal tissues versus placebo tissues in reducing incidence of respiratory illness at 24 weeks. In order to enhance compliance, they elect to randomize families rather than individuals to one of the two intervention groups.

Answers:

The purpose of the study is to evaluate the effectiveness of different guideline implementation strategies in primary dental care. Participating dental practices were randomized to receive one of four different clinical guidelines related to the management of impacted teeth. The primary outcome was the proportion of patients in a practice whose treatment complied with the guideline. [Cluster (dental practice)]

The purpose of the study is to evaluate the effectiveness of a cholesterol screening program intended to lower the risk of cardiovascular mortality in a trial randomizing family practices to either the intervention strategy or a control. The influence of a patient’s level of education on the success of the intervention is also of interest.[Individual]

Investigators wish to evaluate the effectiveness of treated nasal tissues versus placebo tissues in reducing incidence of respiratory illness at 24 weeks. In order to enhance compliance, they elect to randomize families rather than individuals to one of the two intervention groups. [Individual]