Till Roenneberg et al. in Munich, based on more than 25000 questionnaires, have defined chronotypes thusly:

Those who sleep 8 hours starting 20:30 through 00:00 are early types = 46,5 %
Those who sleep 8 hours starting 00:30 or 01:00 are normal = 28,5 %
Those who sleep 8 hours starting 01:30 through 05:30 are late types = 25%

This seems skewed to me. I don't consider those who go to sleep at midnight to be A-persons.

Using the Munich figures in a more reasonable (to me) way:

Those who sleep 8 hours starting 20:30 through 23:00 are early types = 15,0 %
Those who sleep 8 hours starting 23:30 through 00:30 are normal types = 47,5 %
Those who sleep 8 hours starting 01:00 through 05:30 are late types = 37,5 %

What do you think? What's "normal" and what's B?

DSPS, 02 November 2009
My blog: http://delayed2sleep.wordpress.com [1]