The Mathematics Of Murphy’s Law


“If anything can go wrong, it will go wrong. “ is one way to express the famous adage known by such names as Murphy’s Law, Finagle’s Law, and Sod’s Law. Some people consider it a myth while others take it seriously. British mathematician Philip Obadya. working with colleagues David Lewis and Keylan Leyser, came up with a formula that statistically calculates the likelihood of this law. Working with a sample of over 1000 people. Obadya’s equation is:

R_{SL}=\frac{[(U+C+1)\cdot (10-S)]}{20}\cdot\frac{A}{[1-\sin(F/10)]}

To figure out the likelihood of the law occurring. you assign value to the variables in the formula as follows:

U stands for the urgency of a task and is given a value on a scale of 1 and 9, with 9 meaning most urgent.

Similarly for C stands for the complexity of a task and is assigned a value between I and 9.

S represents how skilled you are at performing the task, and also is assigned a value between 1 and 9.

A stands for aggravation. and is a constant. Its value is 0.7, which was determined by polling over 1000 people.

F stands for how frequently you perform the task, and is also assigned a value from 1 to 9.

The Rating of Sod’s Law, RSL, ends up ranging between 0 and 8.6, where the higher number warns you that it’s likely something may happen.

Obadya points out in Null Hypothesis, The Joumal of Unlikely Science that:

The lesson from that, to cut the seemingly unbeatable Sod’s Law Gremlins down to size you need to change one of the elements in the equation […] There is, of course, a Sod’s Law element to using the equation as well. So beware, If you judge your ratings wrongly, you might become too optimistic, allowing calamity to strike. Furthermore, knowing a priori the RSL value of a paI1icular task may well lead to over-confidence, producing a positive feedback mechanism by which the Sod’s Law rating increases still further.

In other words, even the knowledge of the mathematics behind Murphy’s Law will not save you from it!

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My name Edmark M. Law. I work as a freelance writer, mainly writing about science and mathematics. I am an ardent hobbyist. I like to read, solve puzzles, play chess, make origami and play basketball. In addition, I dabble in magic, particularly card magic and other sleight-of-hand type magic. I live in Hong Kong. You can find me on Twitter` and Facebook. My email is

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