Editing Longitudinal study (section)

== Disadvantages ==
Longitudinal studies are time-consuming and expensive.<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]] |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304191937/http://psychology.about.com/od/lindex/g/longitudinal.htm |url-status=dead }}</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 reduction in the research sample will bias the remaining smaller sample.{{cn|date=February 2024}}

Practice effect is also one of the problems: longitudinal studies tend to be influenced because subjects repeat the same procedure many times (potentially introducing [[autocorrelation]]), and this may cause their performance to improve or deteriorate.{{cn|date=February 2024}}