infert <- data.frame(
 education = structure(factor(c(1, 1, 1, 1, 2,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3,
	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 1, 1, 1, 1, 2, 2,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3,
	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 1, 1, 1, 1, 2, 2, 2, 2,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3,
	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3), levels=1:3),
	class = "factor", .Label = c("0-5yrs", "6-11yrs", "12+ yrs")),
 age = c(26, 42, 39, 34, 35, 36, 23, 32,
	21, 28, 29, 37, 31, 29, 31, 27, 30, 26, 25, 44, 40, 35, 28, 36,
	27, 40, 38, 34, 28, 30, 32, 34, 42, 32, 39, 35, 36, 34, 30, 28,
	39, 35, 41, 37, 30, 37, 28, 27, 26, 38, 24, 36, 27, 28, 29, 36,
	28, 28, 28, 27, 35, 25, 34, 31, 26, 32, 21, 28, 37, 25, 32, 25,
	31, 38, 26, 31, 31, 25, 31, 34, 35, 29, 23, 26, 42, 39, 34, 35,
	36, 23, 32, 21, 28, 29, 37, 31, 29, 31, 27, 30, 26, 25, 44, 40,
	35, 28, 36, 27, 40, 38, 34, 28, 30, 32, 34, 42, 32, 39, 35, 36,
	34, 30, 28, 39, 35, 41, 37, 30, 37, 28, 27, 26, 38, 24, 36, 27,
	28, 29, 36, 28, 28, 28, 27, 35, 25, 34, 31, 26, 32, 21, 28, 37,
	25, 32, 25, 31, 26, 31, 31, 25, 31, 34, 35, 29, 23, 26, 42, 39,
	34, 35, 36, 23, 32, 21, 28, 29, 37, 31, 29, 31, 27, 30, 26, 25,
	44, 40, 35, 28, 36, 27, 40, 38, 34, 28, 30, 32, 34, 42, 32, 39,
	35, 36, 34, 30, 28, 39, 35, 41, 37, 30, 37, 28, 27, 26, 38, 24,
	36, 27, 28, 29, 36, 28, 28, 28, 27, 35, 25, 34, 31, 26, 32, 21,
	28, 37, 25, 32, 25, 31, 38, 26, 31, 31, 25, 31, 34, 35, 29, 23),
 parity = c(6, 1, 6, 4, 3, 4, 1, 2, 1, 2, 2, 4, 1, 3, 2, 2,
	5, 1, 3, 1, 1, 2, 2, 1, 2, 2, 2, 3, 4, 4, 1, 2, 1, 2, 1, 2, 1,
	3, 3, 1, 3, 1, 1, 2, 1, 1, 2, 4, 2, 3, 3, 5, 3, 1, 2, 2, 2, 2,
	1, 2, 2, 1, 1, 2, 2, 1, 1, 3, 3, 1, 1, 1, 1, 6, 2, 1, 2, 1, 1,
	1, 2, 1, 1, 6, 1, 6, 4, 3, 4, 1, 2, 1, 2, 2, 4, 1, 3, 2, 2, 5,
	1, 3, 1, 1, 2, 2, 1, 2, 2, 2, 3, 4, 4, 1, 2, 1, 2, 1, 2, 1, 3,
	3, 1, 3, 1, 1, 2, 1, 1, 2, 4, 2, 3, 3, 5, 3, 1, 2, 2, 2, 2, 1,
	2, 2, 1, 1, 2, 2, 1, 1, 3, 3, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 2,
	1, 1, 6, 1, 6, 4, 3, 4, 1, 2, 1, 2, 2, 4, 1, 3, 2, 2, 5, 1, 3,
	1, 1, 2, 2, 1, 2, 2, 2, 3, 4, 4, 1, 2, 1, 2, 1, 2, 1, 3, 3, 1,
	3, 1, 1, 2, 1, 1, 2, 4, 2, 3, 3, 5, 3, 1, 2, 2, 2, 2, 1, 2, 2,
	1, 1, 2, 2, 1, 1, 3, 3, 1, 1, 1, 1, 6, 2, 1, 2, 1, 1, 1, 2, 1, 1),
 induced = c(1, 1, 2, 2, 1, 2, 0, 0, 0, 0, 1, 2, 1, 2, 1,
	2, 2, 0, 2, 0, 0, 2, 0, 0, 1, 0, 0, 0, 1, 2, 0, 1, 1, 0, 1, 0,
	0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 2, 2, 0, 1, 1, 1, 0, 0, 0, 1,
	0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1,
	0, 0, 2, 0, 0, 2, 0, 2, 0, 2, 1, 0, 2, 0, 0, 0, 1, 0, 0, 1, 1,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0,
	2, 0, 1, 1, 0, 0, 0, 1, 0, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2,
	1, 1, 2, 1, 0, 0, 0, 0, 0, 2, 1, 0, 1, 0, 0, 0, 0, 2, 0, 0, 0,
	0, 0, 0, 2, 0, 2, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 1,
	1, 1, 0, 0, 2, 0, 0, 0, 0, 0, 2, 1, 0, 0, 0, 2, 0, 0, 0, 2, 0,
	0, 0, 0, 0, 0, 0, 0, 1, 2, 1, 1, 2, 2, 2, 0, 1, 0, 2, 1, 0, 1,
	1, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 2, 0, 0),
 case = c(rep(1,83), rep(0,165)),
 spontaneous = c(2, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0,
	0, 1, 0, 1, 1, 1, 1, 1, 0, 2, 1, 1, 2, 2, 2, 2, 0, 1, 0, 0, 2,
	0, 2, 1, 2, 0, 1, 2, 0, 0, 1, 0, 0, 2, 0, 0, 2, 2, 2, 1, 1, 2,
	2, 0, 2, 1, 2, 2, 1, 1, 2, 0, 1, 1, 2, 2, 0, 0, 1, 1, 2, 2, 1,
	1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1,
	0, 0, 2, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 2, 1, 0, 0, 0, 0, 0,
	0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0,
	1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 2, 0, 0, 0,
	0, 0, 0, 1, 1, 0, 0, 0, 2, 0, 2, 0, 1, 0, 1, 1, 1, 0, 2, 0, 0,
	2, 0, 1, 0, 0, 0, 0, 1, 2, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0,
	0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0,
	0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 2, 1, 0, 1, 1, 1,0,0,1,1),
 stratum = c(1:83, 1:73, 75:83, 1:83), # one '74' missing
 pooled.stratum = c(3, 1, 4, 2, 32, 36, 6, 22, 5, 19, 20, 37, 9, 29, 21, 18,
	38, 7, 28, 17, 14, 24, 19, 12, 18, 27, 26, 31, 34, 35, 10, 23, 16, 22,
	13, 24, 12, 31, 30, 8, 33, 11, 15, 25, 44, 48, 51, 61, 49, 60, 56, 62,
	57, 42, 52, 55, 51, 51, 42, 50, 54, 41, 47, 53, 49, 46, 39, 58,
	59, 41, 46, 41, 45, 63, 49, 45, 53, 41, 45, 47, 54, 43, 40, 3,
	1, 4, 2, 32, 36, 6, 22, 5, 19, 20, 37, 9, 29, 21, 18, 38, 7,
	28, 17, 14, 24, 19, 12, 18, 27, 26, 31, 34, 35, 10, 23, 16, 22,
	13, 24, 12, 31, 30, 8, 33, 11, 15, 25, 44, 48, 51, 61, 49, 60,
	56, 62, 57, 42, 52, 55, 51, 51, 42, 50, 54, 41, 47, 53, 49, 46,
	39, 58, 59, 41, 46, 41, 45, 49, 45, 53, 41, 45, 47, 54, 43, 40,
	3, 1, 4, 2, 32, 36, 6, 22, 5, 19, 20, 37, 9, 29, 21, 18, 38,
	7, 28, 17, 14, 24, 19, 12, 18, 27, 26, 31, 34, 35, 10, 23, 16,
	22, 13, 24, 12, 31, 30, 8, 33, 11, 15, 25, 44, 48, 51, 61, 49,
	60, 56, 62, 57, 42, 52, 55, 51, 51, 42, 50, 54, 41, 47, 53, 49,
	46, 39, 58, 59, 41, 46, 41, 45, 63, 49, 45, 53, 41, 45, 47, 54, 43, 40)
)