I wouldn't say “balance of probabilities”. It's not a probability. The adjudicators are trained to look at and consider all of the evidence. They may have medical opinions or incident reports, and they may have some that contradict each other or do not clarify. At the end, in some cases in which there is evidence for and against, they weigh it, and then they are to apply the benefit of the doubt.
On October 1st, 2012. See this statement in context.