Description of file carot-longitudinal.dat:

	ptid	= patient id number
	month	= approximate study month
	datey	= year of sample
	datem	= month of sample
	dated	= day of sample
	tm	= time of sample
	ndays	= days since last measurement
	bcarot	= plasma beta carotene
	ret	= plasma retinol
	retpalm	= plasma retinol palmitate
	vite	= plasma vitamin E
	dose	= dose group patient randomized into
	lasty	= year of last dosage administered
	lastm	= month of last dosage administered
	lastd	= day of last dosage administered
	lasttm	= time of last dosage administered


NOTE:

(0)  The values -9, -99 etc. are missing value codes!

(1)  The variable "lasttm" takes the value 0 prior to randomization, 
and after administration of study drug is stopped.

(2)  All patients are on placebo for months 0, 1, 2, and 3.

(3)  The S+ function "julian" can be used to convert date information (but
you should be fine with month for this analysis).