size.ci.slope {statpsych} | R Documentation |
Sample size for a slope confidence interval
Description
Computes the total sample size required to estimate a population slope with desired confidence interval precision in a between-subjects design with a quantitative factor. In an experimental design, the total sample size would be allocated to the levels of the quantitative factor and it might be necessary to increase the total sample size to achieve equal sample sizes. Set the error variance planning value to the largest value within a plausible range for a conservatively large sample size.
Usage
size.ci.slope(alpha, evar, x, w)
Arguments
alpha |
alpha level for 1-alpha confidence |
evar |
planning value of within group (error) variance |
x |
vector of x values of the quantitative factor |
w |
desired confidence interval width |
Value
Returns the required total sample size
Examples
x <- c(2, 5, 8)
size.ci.slope(.05, 31.1, x, 1)
# Should return:
# Total sample size
# 83
[Package statpsych version 1.6.0 Index]