I'm having trouble getting my questionnaire file set up to do the block randomization I'm looking for. I have 20 sets of questions, each with 6 items presented in groups of 3: (a, b, c) or (d, e, f). I want to present participants with one of the (randomly chosen) groups of 3 for each of the 20 sets.

So each participant should get either (1a, 1b, 1c) OR (1d, 1e, 1f), either (2a, 2b, 2c) OR (2d, 2e, 2f), etc., all the way down to either (20a, 20b, 20c) OR (20d, 20e, 20f).



I also would like to randomize the order in which they see the 20 items, so participant 1 might get:
(14a, 14b, 14c); (3d, 3e, 3f); (8d, 8e, 8f); etc.

...and participant 2 might get:
(2d, 2e, 2f); (19d, 19e, 19f); (10a, 10b, 10c); etc.

Does that make sense? I'd rather not have to make each set of 3 questions (e.g., 1a, 1b, 1c) into a separate questionnaire, because then I would need 40 questionnaires just for this randomization!

Any suggestions on how to do this?