Computes the total sample size required to test a population slope with desired power 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 use a larger 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.
size.test.slope(alpha, pow, evar, x, slope, h)alpha level for hypothesis test
desired power
planning value of within-group (error) variance
vector of x values of the quantitative factor
planning value of slope
null hypothesis value of slope
Returns the required total sample size
x <- c(2, 5, 8)
size.test.slope(.05, .9, 31.1, x, .75, 0)
#> Total sample size
#> 100
# Should return:
# Total sample size
# 100