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Table 3 Evaluable sample size estimates

From: A description of the methods of the aspirin supplementation for pregnancy indicated risk reduction in nulliparas (ASPIRIN) study

PTB rate in Placebo Arm

PTB rate in ASA

% Red.

Sample size per group

PTB rate in ASA

% Red.

Sample size per group

PTB rate in ASA

% Red.

Sample size per group

Power = 80% (α = 0.05; β = 0.2)

 8%

4.8%

40%

918

6.0%

25%

2554

6.40%

20%

4096

 10%

6.0%

40%

721

7.5%

25%

2005

8.00%

20%

3213

 12%

7.2%

40%

591

9.0%

25%

1638

9.60%

20%

2625

 14%

8.4%

40%

497

10.0%

25%

1377

11.20%

20%

2204

Power = 90% (α = 0.05; β = 0.1)

 8%

4.8%

40%

1228

6.0%

25%

3419

6.40%

20%

5483

 10%

6.0%

40%

965

7.5%

25%

2683

8.00%

20%

4301

 12%

7.2%

40%

790

9.0%

25%

2193

9.60%

20%

3513

 14%

8.4%

40%

665

10.5%

25%

1842

11.20%

20%

2950