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Table 1 Description of three scenarios of cluster randomized trials presented in survey

From: Variability in research ethics review of cluster randomized trials: a scenario-based survey in three countries

Scenario Description
Cluster-cluster trial (mass media advertising for colorectal cancer screening) A researcher at your institution is proposing a cluster randomized trial to evaluate a radio, television, and billboard advertising campaign aimed at increasing the proportion of community residents who receive colorectal cancer screening according to well-accepted national guidelines. Cluster randomization is used because the intervention (the advertising campaign) is delivered to the community as a whole. Twenty cities will be randomly assigned to either the intervention group or a control group receiving no intervention. A random sample of 500 residents in each city will be surveyed before the intervention, and a separate random sample of 500 residents in each city will be surveyed after the intervention, to determine the proportions that have been screened. The surveys will be conducted by telephone using random digit dialing. No personally identifying information will be collected in the surveys.
Professional-cluster trial (professional education to reduce imaging) A researcher at your institution is proposing a cluster randomized trial to evaluate an educational intervention designed to reduce unnecessary requests for X-rays in accordance with well-accepted national guidelines (which have been widely available for two years) for patients with nontraumatic back and knee pain. All 250 general practices in the study area will be randomly assigned to either the educational intervention or a control group. The guidelines will be mailed to all general practitioners (GPs) in intervention and control practices, but intervention GPs will additionally receive regular reminder messages about the guidelines by mail, as well as feedback about the number of X-rays ordered by their whole practice compared with requests made by all GPs in the study. Study outcome 1 is the number of X-rays ordered per thousand patients using data routinely collected by radiology departments. These data will be sent to the researchers with GP identifiers included, to allow the researchers to prepare feedback to the practices about their number of X-ray requests. Study outcome 2 is the percentage of X-ray requests that are concordant with the guidelines, determined by researchers reviewing and collecting anonymized data from a randomly chosen subset of 100 patient records per practice.
Individual-cluster trial (distribution of bed nets against malaria) A researcher at your institution is proposing a cluster randomized trial to evaluate a malaria prevention intervention. Thirty villages in Cambodia with a total population of 10,000 will be randomly assigned to either an intervention group in which insecticide-treated bed nets will be distributed to all residents (by delivering them to each household), or a control group in which no bed nets will be distributed to any residents. Cluster randomization is used because the bed nets can only be effective in preventing the spread of malaria if they are used by the majority of residents in a village and because the investigators feel that it would not be acceptable to distribute bed nets to only a random half of the residents in a village. Although insecticide-treated bed nets have previously been shown to be effective against malaria in most tropical and subtropical regions, there are differences in vector biting cycles and malaria epidemiology in South East Asia that raise questions about the effectiveness of the insecticide-treated bed nets in Cambodia. Village volunteers in both intervention and control villages will be trained to recognize malaria symptoms and administer standard anti-malarial treatment. Villagers will be told that they can consult the village malaria worker when unwell. Malaria prevalence will be determined before and after the intervention using blood tests from cross-sectional random samples of 250 people per village.