It is not the medieval idea that a full moon drives people insane, at least temporarily, that affects the crime rate. It is simply that the greater light when the moon is full enables criminals to carry out their crimes more easily. A large data sample studied in Bavaria around ten years ago found no association between stages of the moon cycle and violence.
Further Australian studies of hospitalised mental health patients found no correlation between their state and the stage of the moon. Despite persistent beliefs in the power of the moon's phase to affect human behaviour, the evidence counters this belief. A full moon does appear to affect the behaviour of some species of animal however.
Whilst you can probably see a bit better when you go out on a full moon, you are not more likely to get murdered, be in a car accident or be bitten by a rabid dog. Researchers have unearthed no good evidence of a lunar effect, despite earlier flawed findings and ideas promoted by non-scientists. Why has this mythand others about purely coincidental relationshipspersisted? It is because people tend to remember events that confirm their beliefs and ignore those that dont (this is called confirmation bias). So if your house got burgled on a full moon, you will remember it and probably blame a lunatic (pun intended). Despite evidence to the contrary, police departments have been known to put more cops on duty when the moon is full.
Reference: Lilienfeld,S., Lynn,S.J., Ruscio, J., & Beyerstein, B.L. (2010). 50 Great Myths of Popular Psychology: Shattering Widespread Misconceptions About Human Behaviour. Chichester, UK: Wiley-Blackwell*##**##*