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Statistical review: frequently given comments
  1. Stian Lydersen
  1. Correspondence to Professor Stian Lydersen, Regional Centre for Child and Youth Mental Health and Child Welfare, Norwegian University of Science and Technology, Olav Kyrres gate 9, P.O. Box 890, MTFS, Trondheim N-7491, Norway; stian.lydersen{at}


From 2006 to 2014, I have carried out approximately 200 statistical reviews of manuscripts for ARD. My most frequent review comments concern the following:

1. Report how missing data were handled.

2. Limit the number of covariates in regression analyses.

3. Do not use stepwise selection of covariates.

4. Use analysis of covariance (ANCOVA) to adjust for baseline values in randomised controlled trials.

5. Do not use ANCOVA to adjust for baseline values in observational studies.

6. Dichotomising a continuous variable: a bad idea.

7. Student's t test is better than non-parametric tests.

8. Do not use Yates’ continuity correction.

9. Mean (SD) is also relevant for non-normally distributed data.

10. Report estimate, CI and (possibly) p value—in that order of importance.

11. Post hoc power calculations—do not do it.

12. Do not test for baseline imbalances in a randomised controlled trial.

13. Report actual p values with 2 digits, maximum 3 decimals.

14. Format for reporting CIs.

  • Outcomes research
  • Epidemiology
  • Treatment

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