Multiple choice exams and "data forensics"?

Hello - just wanted to get some other peoples' opinions.

My question is regarding data forensic security on large-scale country-wide exams. Are they used fairly consistently or are they fairly cost prohibitive that they use it more as a deterrent or if they observe a candidate that's suspected? I can't seem to find anyone online or in any forums talking about being caught using data forensics or how much it costs to perform data forensics on every candidate.

Thanks.