Table 1. Progesterone indices in ovulatory cycles.

Index	x	y	Sample‡	n	Median	Mean	SEM
mF*	First observed day + 2	-15.5	Bolivia rural: all	118	74	77	3.3
			Bol rural: conceiving	10	74	72	7.5
			Chicago: all	20	92	100	10.1
			Chicago: conceiving	10	122	108	14.6
Mean luteal†	-0.5	-14.5	Bolivia rural: all	118	152	163	5.0
			Bol rural: conceiving	10	143	152	11.6
			Chicago: all	20	268	242	21.5
			Chicago: conceiving	10	311	264	31.6
mPL†	Day of peak -2.5	Day of peak +2.5	Bolivia rural: all	118	222	237	7.5
			Bol rural: conceiving	10	217	209	17.7
			Chicago: all	20	355	336	29.1
			Chicago: conceiving	10	388	363	42.6

Index is defined as (integral of P from x to y)/(y - x); cycles aligned on first day of subsequent cycle; units are pmol/liter.

^*Bolivia rural vs. Chicago ovulatory cycles, Mann-Whitney test, P < 0.02

^†Bolivia rural vs. Chicago ovulatory cycles, Mann-Whitney test, P < 0.002

^‡Within population, ovulatory cycles of conceiving vs. nonconceiving women, Mann-Whitney, not significant