A quit-vaping study randomized groups: identify the clusters

Write the allocation unit next to the count

Cochrane describes cluster trials as assigning groups rather than individual participants. A report can contain many participants while assigning a much smaller number of groups. Record both counts if the paper provides them, and keep each label attached to its unit.

Do not replace a missing cluster count with a guess based on the number of locations mentioned in a news article. Locations, assigned groups and participants can refer to different things. The useful first question is what the researchers actually randomized.

Cochrane: Chapter 23: Including variants on randomized trials

Draw a small conceptual example

Imagine an invented project assigning four community groups to two meeting formats. Each group has several attendees. Drawing four boxes with attendees inside makes the allocation visible: the project assigned boxes, rather than assigning each attendee separately.

This sketch is a reading exercise, not a real vaping trial or a demonstration that four groups would be an adequate design. Do not infer a study’s precision from the picture. The example’s purpose is to keep the group-level assignment distinct from the number of people observed.

Find the analysis explanation

Cochrane emphasizes that these designs need analysis appropriate to their grouping. Look for the report’s description of cluster adjustment or a methods explanation addressing the allocation unit. You do not need to perform the adjustment yourself or correct a published estimate from a headline.

If the material you have does not describe the analysis, write “grouping addressed: not yet verified” and seek the full methods. A missing explanation in a summary does not prove that the researchers ignored the design. Avoid repeating an exact precision claim while its basis remains unclear.

Cochrane: Chapter 23: Including variants on randomized trials

Check whether the setting resembles the decision you face

A group-delivered program may involve an organizer, room or service infrastructure that you do not have. Separate that practical access question from the allocation question. A study assigning groups does not establish the effect of downloading a different app alone at home.

Keep your final note short: allocation unit, participant unit, analysis explanation and remaining question. This guide explains how to recognize a design feature; it does not judge a named trial, rank support programs or make individualized clinical recommendations. For personal care decisions, discuss the actual evidence and circumstances with qualified support.