I believe probability and statistics ignore a fundamental aspect of reality. Uniqueness. Everything is unique in every moment. All the variables cannot be seen, understood and calculated (yet). Putting any faith in statistical probabilities is just that, Faith. Given our limited abilities any jugdements based on statisics should be taken with a grain of salt. The less variables factored in the less Faith one should have in the informations validity. In the case of treatment A or B in the example, if this is all the information you have to go on I'd probably tossing a coin.