The power of the Z statistic: Implications for trauma research and quality assurance review

Eric M. Cottington, Charles M. Shufflebarger, Ricard Townsend

Research output: Contribution to journalArticle

17 Scopus citations


The Z statistic can be used to test whether the observed number of survivors in a specific trauma population is significantly different from what would be expected based on the Major Trauma Outcome Study (MTOS) norms. However, as with any statistic, inferences based on the Z statistic should be made with care. This is particularly true when a non-significant Z statistic is observed. The purpose of this paper, using data from a large, urban trauma registry, is to illustrate how the power of the Z statistic, or its ability to detect a difference between observed and expected survival, is influenced by the magnitude of the difference, the direction of the difference, the survival probability distribution of the study population, and the sample size. The implications for trauma research and quality assurance review are discussed.

Original languageEnglish (US)
Pages (from-to)1500-1509
Number of pages10
JournalJournal of Trauma - Injury, Infection and Critical Care
Issue number11
StatePublished - Nov 1989


ASJC Scopus subject areas

  • Surgery
  • Critical Care and Intensive Care Medicine

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