%0 Journal Article %T Hypothesis testing and the error of the third kind %A Dieter Rasch %J Psychological Test and Assessment Modeling %D 2012 %I Pabst Science Publishers %X In this note it is shown that the concept of an error of the third kind (type-III-error) stems from a wrong understanding of the concept of hypothesis testing in mathematical statistics. If the alterna-tive hypothesis in a statistical testing problem states that the null hypothesis is wrong, then an error of the third kind cannot occur. This error can only be defined in more-decision-problems, i.e. prob-lems where we have to decide for one of more than two possibilities. Further the problem of the power of tests between a null and an alternative hypothesis is discussed. The notation of set theory is used because it allows for a concise notation of this type of statistical testing problems. The notation is explained in an appendix. %K Hypothesis testing %K more-decision-problems %K Neyman-Pearson Theory %K power of a test %U http://www.psychologie-aktuell.com/fileadmin/download/ptam/1-2012_20120326/06_Rasch.pdf