title: The power of the Z statistic: implications for trauma research and quality assurance review.
abstract: 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.
authors.affiliation: Allegheny-Singer Research Institute, Pittsburgh, PA 15212-9986.
authors.forename: E M
authors.initials: EM
authors.lastname: Cottington
authors.forename: C M
authors.initials: CM
authors.lastname: Shufflebarger
authors.forename: R
authors.initials: R
authors.lastname: Townsend
mesh_terms: D006259:Craniocerebral Trauma / Q000401:mortality; D006302:Health Services Research / Q000706:statistics & numerical data*; D006746:Hospital Bed Capacity, 500 and over; D006801:Humans; D015601:Injury Severity Score; D008722:Methods; D010414:Pennsylvania; D011336:Probability; D011785:Quality Assurance, Health Care / Q000706:statistics & numerical data*; D012042:Registries; D012189:Retrospective Studies; D016019:Survival Analysis; D013898:Thoracic Injuries / Q000401:mortality; D015599:Trauma Severity Indices; D014947:Wounds and Injuries / Q000401:mortality*