Increased transparency was required when reporting imputation of primary outcome data in clinical trials

The aim of this study is to explore the transparency of reporting primary outcome data within randomized controlled trials in the presence of missing data.

A cohort examination of randomized controlled trials published in the four major medical journals (NEJM, JAMA, BMJ, Lancet) in 2013 and the first quarter of 2018. Data were extracted on reporting quality, the number of randomized participants, and the number of participants included within the primary outcome analysis with observed or imputed data.

Ninety-one of 159 (57%) studies analyzed from 2013 and 19 of 46 (41%) from 2018 included imputed data within the primary outcome analysis. Of these, only 13 of 91 (14%) studies from 2013 and 1 of 19 (5%) studies from 2018 explicitly reported the number of imputed values in the CONSORT diagram. Results' tables included levels of imputed data in 12 of 91 (13%) studies in 2013 and 4 of 19 (21%) in 2018. Consequently, identification of imputed data was a time-consuming task requiring extensive cross-referencing of all manuscript elements.

Imputed primary outcome data are poorly reported. Participant flow diagrams frequently reported participant status which does not necessarily correlate to availability of data. We recommended that the number of imputed values are explicitly reported within CONSORT flow diagrams to increase transparency.