Remember kids... always wear a helmet. (The almighty bikeradar helmet thread)

Jokes aside, this is why we ignore anecdote and study populations; if you measure the passing distance enough times, you get a statistically significant view of whether some factors relating to the cyclist influence the behaviour of a population of drivers. Of course, some drivers pass wide and slow regardless of who is riding, and some seem determined to clip your elbow with their wing mirror whatever you're wearing, but the distribution curve does seem to shift slightly according to cues which inform the driver about the perceived expertise of the cyclist. If you've ever been circumspect when passing a Boris Bike, you've experienced the effect.

Makes sense. Also explain why drivers pass me with such little room (a narrow 'birth' if you will) even though I am not wearing a helmet. It must be clear even to the non-cyclist car driver how darn good a cyclist I am.