 በውስጥ-ታሪፍ ንድፍ የተሻሻለ የስታቲስቲክስ ትንበያን ያቀርባሉ, ነገር ግን ሊፈጠሩ የሚችሉ ክፍተቶች (ለምሳሌ, ቅድመ-ህክምና እና የሕክምና ጊዜያት መካከል የአየር ሁኔታ ለውጦች) (Greenwald 1976; Charness, Gneezy, and Kuhn 2012).
Mkati-nkhani machenjerero kupereka bwino zowerengera mwandondomeko kuchotsa pakati pa nkhani kusiyanitsa (onani zaumisiri Zakumapeto), koma lotseguka kwa confounders kotheka (mwachitsanzo, kusintha nyengo pakati pa chisanadze mankhwala ndi mankhwala nthawi) (Greenwald 1976; Charness, Gneezy, and Kuhn 2012).