I have an experiment where each participant was presented with 20 questions, and for each had to choose their preferred answer from 2 given options. The options were generated from 2 different categories. I'm trying to investigate whether there was consistency in each user's choices between categories, i.e. whether users tend to pick from the same category more often than chance (no matter which of the two categories they tend towards). However, I have no idea how to test this. I can't just do a one-sample t-test, because that would just test whether users prefer one specific category over the other overall. It seems like I'm maybe looking to test whether there are two modes in the distribution, for picking one category over the other?