SomeLongitudinal of the disadvantages of longitudinal study are that theystudies are time-consuming and expensive. Therefore, they are not convenient.<ref name="Longitudinal study">{{cite web |last=Cherry |first=Kendra |title=What Is Longitudinal Research? |url=http://psychology.about.com/od/lindex/g/longitudinal.htm |access-date=22 February 2012 |website=[[About.com]]}}</ref>
Longitudinal studies cannot avoid an attrition effect,: that is, some subjects cannot continue to participate in the study for various reasons. Under longitudinal research methods, the lossreduction ofin the research sample will bias the remaining smallsmaller sample.
Practice effect is also one of the problems.: Longitudinallongitudinal studies tend to be biasedinfluenced by the fact thatbecause subjects repeat the same procedure many times (potentially introducing [[autocorrelation]]), and this may cause their performance will beto improvedimprove or decreaseddeteriorate.
