Posted by JSegal on April 11, 2003 at 13:59:16:In Reply to: Re: Assessing Roadworthiness posted by zzz in Ottawa on April 11, 2003 at 10:59:28:
Here's the long answer. I hope it helps.
I confess to not having read the orignal paper, but a review in AARC Times, April 2000 by Cameron Harris quotes a multicenter study by Doghramji et al: A normative study of the MWT. Electroencephalogyaphy and Clinical Neurophysiology 103 (5) 554-562.
The protocol calls for:
Illumination at 0.1-0.13 lux (= to a 7.5 W )night light, unlike the MSLT which requires total darkness.Pt is in the sitting position with a back cushion to support the head. A comfortable lounge chair which can elevate the legs is OK.The pt is told " Please sit still and remain awake for as long as you can". They should not use extreme measures to stay awake (such as vocalizing or self-inflicting pain)
4 naps, starting at 10am at 2 hour intervals are done. The naps opportunities can be either 20min or 40min each.The naps are terminated when sleep occurs.
For the 20min protocol the normal is 18.1 +/-3.6min. So 95% of pts should stay awake more than 18.1 -(2*3.6) = 10.9 min and 95% of subjects will have a value less than 18.1 + (2*3.6)= 25.3 min (although I don't know how this could be since the nap opportunities don't go beyond 20 min.)
On the 40 min protocol the reported normal is 32.6 +/- 9.9 min. So 95% of subjects will stay awake beyond 12.8 min, and 95% will fall asleep within 52.4min statistically.
The article says that for practical purposes the 40 min protocol is probably preferable as many people stay awake beyond 20min. If you use 1 std deviation below the mean as the cut-offDr Harris points out that only 15% of the populaiton will have MWTs below 22 min.