I put Decisions API against classic statistics experiments: (1) loaded coin, and (2) marble selection from a jar, with replacement. I tested both predicate and choice questions. I ran thousand trials against each experiment, and I also did an experiment where I change the order of choices, to see if it matters. Summary:

* Using predicate questions gave nearly perfect/expected probability outcomes

* Asking it to choose an outcome behaved differently from drawing randomly - if the true probability of a red marble draw was 50%, using Decisions API produced 86%, i.e. it picked the right marble but gave a significantly more biased weight on its choice

* Changing the choice order changes the probabilities! Moving the red marble from first to last choice changed its probability estimate from 86% to 73%