ssLong.multiTime: Sample size calculation for testing if mean changes for 2...

Description Usage Arguments Details Value Note Author(s) References See Also Examples

Description

Sample size calculation for testing if mean changes for 2 groups are the same or not for longitudinal study with more than 2 time points.

Usage

1
ssLong.multiTime(es, power, nn, sx2, rho = 0.5, alpha = 0.05)

Arguments

es

effect size

power

power

nn

number of observations per subject

sx2

within subject variance

rho

within subject correlation

alpha

type I error rate

Details

We are interested in comparing the slopes of the 2 groups A and B:

β_{1A} = β_{1B}

where

Y_{ijA}=β_{0A}+β_{1A} x_{jA} + ε_{ijA}, j=1, …, nn; i=1, …, m

and

Y_{ijB}=β_{0B}+β_{1B} x_{jB} + ε_{ijB}, j=1, …, nn; i=1, …, m

The sample size calculation formula is (Equation on page 30 of Diggle et al. (1994)):

m=\frac{2≤ft(Z_{1-α}+z_{power}\right)^2 ≤ft(1-ρ\right)}{ nn s_x^2 es^2}

where es=d/σ, d is the meaninful differnce of interest, sigma^2 is the variance of the random error, ρ is the within-subject correlation, and s_x^2 is the within-subject variance.

Value

subject per group

Note

The test is a two-sided test. For one-sided tests, please double the significance level. For example, you can set alpha=0.10 to obtain one-sided test at 5% significance level.

Author(s)

Weiliang Qiu stwxq@channing.harvard.edu

References

Diggle PJ, Liang KY, and Zeger SL (1994). Analysis of Longitundinal Data. page 30. Clarendon Press, Oxford

See Also

powerLong.multiTime

Examples

1
2
# subject per group = 196
ssLong.multiTime(es=0.5/10, power=0.8, nn=3, sx2=4.22, rho = 0.5, alpha=0.05)

powerMediation documentation built on March 24, 2021, 1:06 a.m.