Description Usage Arguments Details Value Note Author(s) References See Also Examples
View source: R/powerLogisticsReg.R
Calculating sample size for simple logistic regression with binary predictor.
1 2 3 4 5  SSizeLogisticBin(p1,
p2,
B,
alpha = 0.05,
power = 0.8)

p1 
pr(diseased  X = 0), i.e. the event rate at X = 0 in logistic regression logit(p) = a + b X, where X is the binary predictor. 
p2 
pr(diseased  X = 1), the event rate at X = 1 in logistic regression logit(p) = a + b X, where X is the binary predictor. 
B 
pr(X = 1), i.e. proportion of the sample with X = 1 
alpha 
Type I error rate. 
power 
power for testing if the odds ratio is equal to one. 
The logistic regression mode is
\log(p / (1  p)) = β_0 + β_1 X
where p = prob(Y = 1), X is the binary predictor, p_1 = pr(diseased  X = 0), p_2 = pr(diseased X = 1), B = pr(X = 1), and p = (1  B) p_1 + B p_2. The sample size formula we used for testing if β_1 = 0, is Formula (2) in Hsieh et al. (1998):
n=(Z_{1α/2}[p(1p)/B]^{1/2} + Z_{power}[p_1(1p_1)+p_2(1p_2)(1B)/B]^{1/2})^2/[ (p_1p_2)^2 (1B) ]
where n is the required total sample size and Z_u is the uth percentile of the standard normal distribution.
total sample size required.
The test is a twosided test. For onesided tests, please double the
significance level. For example, you can set alpha=0.10
to obtain onesided test at 5% significance level.
Weiliang Qiu stwxq@channing.harvard.edu
Hsieh, FY, Bloch, DA, and Larsen, MD. A SIMPLE METHOD OF SAMPLE SIZE CALCULATION FOR LINEAR AND LOGISTIC REGRESSION. Statistics in Medicine. 1998; 17:16231634.
1 2 3 4  ## Example in Table I Design (Balanced design with high event rates)
## of Hsieh et al. (1998 )
## the sample size is 1281
SSizeLogisticBin(p1 = 0.4, p2 = 0.5, B = 0.5, alpha = 0.05, power = 0.95)

[1] 1281
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