Just for clarity: statistics were not used in the Letby prosecution.

The problem with Letby is that a serial killer was able to hide because finding a rare event (a member of staff murdering multiple babies) is hard to do in the noise (the mish mash of data available).

Currently the English NHS is moving away from SIRI (Serious Incident Requiring Investigation) to PSIRF (Patient Safety Incident Response Framework) which focuses a lot more on "no blame" and "open culture", so it's important that NHS Trusts get the stats right to be able to detect and understand these very rare events.