Munirih Qualls|Daniel J. Pallin|Jeremiah D. Schuur
Parametric Versus Nonparametric Statistical Tests: The Length of Stay Example
Brigham and Women's Hospital|JDSU (United States)|Harvard University|Boston Children's Hospital|Brigham and Women's Hospital|JDSU (United States)|Harvard University|Boston Children's Hospital|Brigham and Women's Hospital|JDSU (United States)|Harvard University|Boston Children's Hospital
study examined selected effects proper use nonparametric inferential statistical methods analysis nonnormally distributed data exemplified emergency department length stay ed los hypothesis parametric methods used inappropriately evaluation ed los recent studies leading emergency medicine em journals illustrate methodologic flaw avoided demonstration using data national hospital ambulatory medical care survey nhamcs presented demonstration shows inappropriate analysis ed los increases probability type ii errorsfive major em journals reviewed january 1 2004 december 31 2007 studies ed los one reported outcomes reviewed authors determined whether ed los analyzed correctly ascertaining whether nonparametric tests used indicated illustrative analysis ed los constructed using 2006 nhamcs data demonstrate inferential testing statistical significance deliver differing conclusions depending whether nonparametric methods used indicatedfortynine articles identified studied ed los 80 perform test normality ed los data data normally distributed 10 studies perform tests overall 43 failed use appropriate nonparametric methods analysis nhamcs data confirmed failure use nonparametric bivariate tests results type ii statistical error multivariate models less explanatory power smaller r valueed los key ed operational metric frequently analyzed incorrectly em literature applying parametric statistical tests nonnormally distributed data reduces power increases probability type ii error failure find true associations appropriate use nonparametric statistics core component statistical literacy use increases validity ed research quality improvement projects