an acronym for reasons that lead to low internal validity

  • Testing – subjects react on the experimental setup or task
  • History – e.g. events between two measurements
  • Instrument – e.g. change of the measurement tool
  • Statistical regression (toward the mean) – data outliers e.g. caused by inhomogeneous test groups
  • Maturation – subjects’ change between two measurements
  • Experimental mortality – subjects‘ disappear
  • Selection – lacking randomization of the tested sample
  • Selective interaction- sequence/order effects