Table for determining sample size from a given population
N S N S N S
5 5 220 140 1200 291
10 10 230 144 1300 297
15 14 240 148 1400 302
20 19 250 152 1500 306
25 24 260 155 1600 310
30 28 270 159 1700 313
35 32 280 162 1800 317
40 36 290 165 1900 320
45 40 300 169 2000 322
50 44 320 175 2200 327
55 48 340 181 2400 331
60 52 380 186 2600 335
65 56 382 191 2800 338
70 59 384 192 3000 341
75 63 400 196 3500 346
80 66 420 201 4000 351
85 70 440 205 4500 354
90 73 460 210 5000 357
95 76 480 214 6000 361
100 80 500 217 7000 364
110 86 550 226 8000 367
120 92 600 234 9000 368
130 97 650 242 10000 370
140 103 700 248 15000 375
150 108 750 254 20000 377
160 113 800 260 30000 379
170 118 850 265 40000 380
180 123 900 269 50000 381
190 127 950 274 75000 382
200 132 1000 278 100000 382
210 136 1100 285 1000000 384

N is the population size.
S is the sample size.


Clearly, sampling within classrooms is not appropriate for program evaluation purposes. However, sampling on small populations (such as a classroom) may be used for other purposes. Exploratory or pilot studies may give indications or hunches which can then be studied more thoroughly with the larger groups. Groups of between 10 and 30 can be used advantageously for such purposes and are easier to handle computationally.