You are not currently logged in.
Access your personal account or get JSTOR access through your library or other institution:
If You Use a Screen ReaderThis content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Comparability of Randomised Groups
Douglas G. Altman
Journal of the Royal Statistical Society. Series D (The Statistician)
Vol. 34, No. 1, Statistics in Health (1985), pp. 125-136
Stable URL: http://www.jstor.org/stable/2987510
Page Count: 12
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Preview not available
Randomised allocation in a clinical trial does not guarantee that the treatment groups are comparable with respect to baseline characteristics. It is common for differences between treatment groups to be assessed by significance tests but such tests only assess the correctness of the randomisation, not whether any observed imbalances between the groups might have affected the results of the trial. In particular, it is quite unjustified to conclude that variables that are not significantly differently distributed between groups cannot have affected the results of the trial. The possible effect of imbalance in a prognostic factor is considered, and it is shown that non-significant imbalances can exert a strong influence on the observed result of the trial, even when the risk associated with the factor is not all that great. It is suggested that comparability should be assessed partly on the basis of clinical knowledge and that it is wise to investigate whether any imbalances between the groups could have had an affect by reanalysing the data taking such factors into account. The implications for trial design are considered briefly.
Journal of the Royal Statistical Society. Series D (The Statistician) © 1985 Royal Statistical Society