How to check the data is generated by machine or human? I have a bunch of data points (about 300 samples in total), each sample is a number from 1 to 3 (from {1, 2, 3}).
These numbers are supposed to come from a survey. Are there any statistical methods to determine whether these sample are generated by human graders, or are they machine generated?

There are many ways in which this could go wrong in real life, but given that it sounds like a test question for students, conceptually simplifying it is a reasonable thing to do. If the survey questions had been randomized (such that the answers (1,2, or 3) were equally likely, this would be a situation where run length testing would be useful.
https://www.itl.nist.gov/div898/handbook/eda/section3/eda35d.htm
