power.2p.2n: Calculate the Power and Sample Size for 2 Independent...

In biostats101: Practical Functions for Biostatistics Beginners

Calculate the Power and Sample Size for 2 Independent Proportions.

Description

This function calculates

1. The power given independent proportions p1 and p2, the sample sizes for the two groups, the confidence level and the alternative hypothesis.

2. The required sample size given independent proportions p1 and p2, the desired power, the confidence level and the alternative hypothesis.

3. The required sample sizes n1 and n2 given the desired power, a sample size ratio n2/n1 (unbalanced designs), the confidence level and the alternative hypothesis.

4. The sample size for the second group given independent proportions p1 and p2, the sample size for the first group (unbalanced designs), the desired power, the confidence level and the alternative hypothesis.

Usage

power.2p.2n(
  p1,
  p2,
  n1 = NULL,
  n2 = NULL,
  nratio = NULL,
  power = NULL,
  alternative = "two.sided",
  conf.level = 0.95,
  continuity = FALSE
)

Arguments

p1	Numeric, the proportion for the first group.
p2	Numeric, the proportion for the second group.
n1	Numeric, the sample size for the first group.
n2	Numeric, the sample size for the second group.
nratio	Numeric, the sample size ratio (n2 / n1) for unbalanced designs. Default is 1 when calculating sample sizes n1 and n2.
power	Numeric, the desired power (1 - beta). Default is 0.8 when calculating sample sizes n1 and n2 and when calculating n2 given n1.
alternative	Character, the type of alternative hypothesis. Options are 'two.sided' (default) or 'one.sided'.
conf.level	Numeric, the confidence level (1 - alpha). Default is 0.95.
continuity	Logical, indicating whether the continuity correction should be applied. Default is FALSE.

Value

A list with the following components:

• n: Total sample size (n1 + n2).

• n1: Sample size for the first group.

• n2: Sample size for the second group.

• power: The estimated power.

• nratio: The sample size ratio (n2 / n1), if applicable.

References

Levin, B., & Chen, X. (1999). Is the one-half continuity correction used once or twice to derive a well-known approximate sample size formula to compare two independent binomial distributions?. The American Statistician, 53(1), 62-66. https://doi.org/10.1080/00031305.1999.10474431. Fleiss, J. L., Levin, B., & Paik, M. C. (2013). Statistical methods for rates and proportions. John Wiley & Sons.

Examples

# Calculate the power for independent proportions given the sample sizes
power.2p.2n(p1 = 0.45, p2 = 0.6, n1 = 260, n2 = 130)

# Calculate the sample size for independent proportions (default power = 0.8)
power.2p.2n(p1 = 0.45, p2 = 0.6)

# Calculate n1 and n2 for independent proportions with ratio n2/n1
power.2p.2n(p1 = 0.44, p2 = 0.6, nratio = 2)

# Calculate n2 given n1 for independent proportions
power.2p.2n(p1 = 0.44, p2 = 0.6, n1 = 108)

biostats101 documentation built on Sept. 13, 2024, 1:11 a.m.