size.test.slope {statpsych}

Sample size for a test of a slope

Description

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.

Usage

size.test.slope(alpha, pow, evar, x, slope, h)

Arguments

alpha

alpha level for hypothesis test

pow

desired power

evar

planning value of within-group (error) variance

x

vector of x values of the quantitative factor

slope

planning value of slope

h

null hypothesis value of slope

Value

Returns the required total sample size

Examples

x <- c(2, 5, 8)
size.test.slope(.05, .9, 31.1, x, .75, 0)

# Should return:
# Total sample size
#               100