Statistical Methods in Medical Research 4ed

758 Appendix tables
Table A8 Sample size for comparing two proportions
This table is used to determine the sample size necessary to find a significant difference (5% two-sided
significance level) between two proportions estimated from independent samples where the true
proportions are p1 and p2, and d ˆ p1 p2 is the specified difference …p1 > p2†. Sample sizes are
given for 90% power (upper value of pair) and 80% power (lower value). The sample size given in the
table refers to each of the two independent samples. The table is derived using (4.42) with a continuity
correction.
Note: If p2 > 0 5, work with p0 1 ˆ 1 p2 and p0 2 ˆ 1 p1.
Smaller
probability,
d ˆ p1 p2
p2 0 05 0 1 0 15 0 2 0 25 0 3 0 3 5 0 4 0 45 0 5
0 05 621 207 11375 54 42 327 2319
475 160 88 59 43 327 22 19 16
0 1 958 286 146 92 65 48 38 30 25 21
726 219 113 72 51 38 30 24 20 17
0 15 1252 354 174 106 73 54 41 33 27 22
946 270 134 82 57 42 33 26 21 18
0 2 1504 412 198 118 80 58 44 34 28 23
1134 313 151 91 62 45 35 27 22 18
0 25 1714 459 216 127 85 61 46 35 28 23
1291 349 165 98 66 47 36 28 23 18
0 3 1883 496 230 134 88 62 46 36 28 23
1417 376 176 103 68 49 36 28 23 18
0 35 2009 522 240 138 90 63 46 35 28 22
1511 396 183 106 69 49 36 28 22 18
0 4 2093 538 244 139 90 62 46 34 27 21
1574 407 186 107 69 49 36 27 21 17
0 45 2135 543 244 138 88 61 44 33 25 19
1605 411 186 106 68 47 35 26 20 16
0 5 2135 538 240 134 85 58 41 30 23 18
1605 407 18310366 45 3 24 19 15