title: The experimental design of postmortem studies: the effect size and statistical power.
abstract: OBJECTIVE
  The aim is of this study was to show the poor statistical power of postmortem studies. Further, this study aimed to find an estimate of the effect size for postmortem studies in order to show the importance of this parameter. This can be an aid in performing power analysis to determine a minimal sample size.
  
  
  METHODS
  GPower was used to perform calculations on sample size, effect size, and statistical power. The minimal significance (α) and statistical power (1 - β) were set at 0.05 and 0.80 respectively. Calculations were performed for two groups (Student's t-distribution) and multiple groups (one-way ANOVA; F-distribution).
  
  
  RESULTS
  In this study, an average effect size of 0.46 was found (n = 22; SD = 0.30). Using this value to calculate the statistical power of another group of postmortem studies (n = 5) revealed that the average statistical power of these studies was poor (1 - β < 0.80).
  
  
  CONCLUSIONS
  The probability of a type-II error in postmortem studies is considerable. In order to enhance statistical power of postmortem studies, power analysis should be performed in which the effect size found in this study can be used as a guideline.
authors.affiliation: Department of BioAnalytical Chemistry, VU University Amsterdam, De Boelelaan, 1081 HV, Amsterdam, The Netherlands. j.meurs@student.vu.nl.
authors.forename: Joris
authors.identifier: http://orcid.org/0000-0002-0288-0422
authors.initials: J
authors.lastname: Meurs
mesh_terms: D003627:Data Interpretation, Statistical; D005554:Forensic Medicine; D006801:Humans; D012107:Research Design; D013223:Statistics as Topic
keywords: Effect size; Experimental design; Postmortem research; Power; Sample size; Significance