Scientists working for British Gas have created a mathematical formula describing Murphy's Law: NEWS.com.au | How you can break Murphy's Law (October 8, 2004).
...a panel of experts has provided the statistical rule for predicting the law of "anything that can go wrong, will go wrong" - or ((U C I) x (10-S))/20 x A x 1/(1-sin(F/10)). [...] In the calculation, five factors have to be assessed: urgency (U), complexity (C), importance (I), skill (S) and frequency (F), and each given a score between one and nine. A sixth, aggravation (A), was set at 0.7 by the experts after their poll.So if you want to decrease your chance of failure in any given situation, see which of the variables you can adjust.