Tim Hunt

"Other LMSs are worse" is not a good defense of Moodle's UI

Rather than making Quiz 2, can't you just let students have two attempts and Quiz 1?

You have indeed found a bug. Would you like to report it in the Moodle Tracker?

(Note to self, the bug is in question_variant_pseudorandom_no_repeats_strategy. The pseudo-random bit needs to include the quiz id or something like that.)

Some docs here: http://docs.moodle.org/23/en/Quiz_statistics_report, but acutally it does not explain.

I had to read the code, it seems to be testing whether Discriminative efficiency < 15%.

http://docs.moodle.org/dev/Quiz_statistics_calculations gives more details.

Try

global $PAGE;

print_object($PAGE->category);

print_object($PAGE->categories);

If you get an error, then "everything" must not have been initialised yet in your script, so try moving that code later. (I think the necessary initialisation happens in require_login).

In the Moodle UI, go to Admin -> Development -> XMLDB, and click the [Doc] link. That shows you the complete DB structure.