One source of bias in 'disabling' incidents is that the cyclist is frequently taken way in an ambulance while police arrive to interview the motorist. They then have their impression of what happened all written up or at least set in their mind before they ever get around to checking with the cyclist.

A close friend was involved in a left-hook incident. He entered the intersection just as the light turned yellow and a motorist who had been waiting to turn hit the gas and turned directly into him. The motorist claimed to have made the turn on a green arrow and that's what the officer had written down in his report when he got to the hospital to talk to my friend. On seeing him in the ER the officer's first comment was that if he hadn't been so injured he'd write him a citation for running a red. It took lots of convincing by my friend to get the officer to understand that a green arrow only appears at that intersection at the beginning of the green cycle, not the end and that the story by the motorist was inconsistent.

These days many traffic light controllers are more clever and sometimes change the sequence in which case the officer would probably still believe the motorist's version. It's much harder to change someone's mind about what happened after they already think they know what did.