Examples

See figure 1, figure 2, and figure 3.

 

Fig 1 CONSORT 2025 flow diagram. Flow diagram of participant progress through the phases of a two group, parallel randomised trial (ie, enrolment, intervention allocation, follow-up, and data analysis). CONSORT=Consolidated Standards of Reporting Trials

 

Fig 2 Flow diagram of a multicentre trial of total (TKR) versus partial (PKR) knee replacement [421]

 

Fig 3 Flow diagram of a multicentre trial of glucocorticoid intradiscal injection in patients with chronic low back pain.422 ESR=erythrocyte sedimentation rate; GC IDI=glucocorticoid intradiscal injection; MRI=magnetic resonance imaging

 

Explanation

The design and conduct of some randomised trials are straightforward, and the flow of participants, particularly where there are no losses to follow-up or exclusions, through each phase of the study can be described relatively easily. For other trials, it can be difficult for readers to discern whether and why some participants did not receive the treatment as allocated, were lost to follow-up, or were excluded from the analysis [423]. This information is crucial for several reasons. Participants who were excluded after allocation are unlikely to be representative of all participants in the study. For example, participants may not be available for follow-up evaluation because they experienced an acute exacerbation of their illness or harms of treatment [271, 424].

 

Attrition as a result of loss to follow-up, which is often unavoidable, needs to be distinguished from investigator-determined exclusion for such reasons as ineligibility, withdrawal from treatment, and poor adherence to the trial protocol. Erroneous conclusions can be reached if participants are excluded from analysis, and imbalances in such omissions between groups may be especially indicative of bias [424-426]. Information about whether the investigators included in the analysis all participants who underwent randomisation, in the groups to which they were originally allocated (item 21b), is therefore of particular importance. Knowing the number of participants who did not receive the intervention as allocated or did not complete treatment permits the reader to assess to what extent the estimated efficacy of therapy might be underestimated in comparison with ideal circumstances.

 

If available, the number of people assessed for eligibility, and reason for exclusion, should also be reported. Although this number is relevant to external validity only and is arguably less important than the other counts,[427] it is a useful indicator of whether trial participants were likely to be representative of all eligible participants.

 

A suggested template for reporting the number of participants who were randomly assigned, received intended treatment, were lost to follow-up, and were analysed for the primary outcome is shown in figure 1, and the counts required are described in detail in table 7. A review of randomised trials published in general medical journals found that reporting of what happened to participants and their data was considerably more thorough in articles that included a diagram of the flow of participants through a trial than in those that did not [423].