Math tasks ordered by difficulty level for GMAT / GRE / SAT

Thank you very much for your answers. I appreciate it.

I'm exactly looking for the b-value in IRT term as you said. The statistics of the math questions of this forum looks interesting. Is there also a sorted list of math tasks available (by category and difficulty)? Or perhaps as a database? Why is there an enormous sample bias?

Do you know if there is an average time limit for SAT, ACT and GRE like the two-minute limit for GMAT?

By the way, if there is a pool of data available for GMAT, GRE, SAT or ACT I could calculate the difficulty level by myself using IRT.

There are several potential sources of bias. The participants on this forum aren't likely to be a representative random sample of test takers in general, for one thing - for example, anyone here has to have a certain level of commitment to their preparation that not all test takers have. And when you look at individual questions posted here, it's not the case that every forum member answers every question. I have no idea who does answer the questions, but the questions are flagged with an estimated difficulty level, and I'd imagine it's possible that higher level test takers often don't bother attempting easy questions, and that lower level test takers often don't bother attempting harder questions. And since there are no consequences for a wrong answer, some people possibly aren't treating questions here as seriously as they would if the question were on a test.

I've never seen any officially published data on test questions from any of the major tests; as far as I know, that information has always been kept confidential. I did see an IRT research paper from several years ago, and the authors of that paper had used a batch of real GMAT questions, along with the relevant item statistics, which I think they had acquired directly from the test developer, but I'd have to go back to the paper to confirm.

It's been a long time since I've looked at either the SAT or ACT tests. The GRE is a faster test than the GMAT, about 90 seconds per Quant question, but the questions are also more straightforward.

Can you share any details about the research you're conducting?