Sample sizes and statistical methods in interventional studies on individuals with spinal cord injury: A systematic review

Georg Zimmermann*, Lisa Maria Bolter, Ronny Sluka, Yvonne Höller, Arne C. Bathke, Aljoscha Thomschewski, Stefan Leis, Simona Lattanzi, Francesco Brigo, Eugen Trinka

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


Aim: Prevalence and incidence of spinal cord injury (SCI) are low. However, sample sizes have not been systematically examined yet, although this might represent useful information for study planning and power considerations. Therefore, our objective was to determine the median sample size in clinical trials on SCI individuals. Moreover, within small-sample size studies, statistical methods and awareness of potential problems regarding small samples were examined. Methods: We systematically reviewed all studies on human SCI individuals published between 2014 and 2015, where the effect of an intervention on one or more health-related outcomes was assessed by means of a hypothesis test. If at least one group had a size <20, the study was classified as a small sample size study. PubMed was searched for eligible studies; subsequently, data on sample sizes and statistical methods were extracted and summarized descriptively. Results: Out of 8897 studies 207 were included. Median total sample size was 18 (range 4-582). Small sample sizes were found in 167/207 (81%) studies, resulting limitations and implications for statistical analyses were mentioned in 109/167 (65%) studies. Conclusions: Although most recent SCI trials have been conducted with small samples, the consequences on statistical analysis methods and the validity of the results are rarely acknowledged.

Original languageEnglish
Pages (from-to)200-208
Number of pages9
JournalJournal of Evidence-Based Medicine
Issue number3
Publication statusPublished - 2019
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2019 The Authors. Journal of Evidence-Based Medicine published by Chinese Cochrane Center, West China Hospital of Sichuan University and John Wiley & Sons Australia, Ltd

Other keywords

  • effect size
  • power
  • rare disease
  • spinal cord trauma
  • statistical data analysis


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