Sample size for a conditional mean confidence interval

Computes the total sample size required to estimate a population conditional mean of y at x = x* in a fixed-x linear regression model with desired confidence interval precision. 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 give the desired sample size at each level of the fixed factor. Set the error variance planning value to the largest value within a plausible range for a conservatively large sample size.

For more details, see Section 1.24 of Bonett (2021, Volume 2)

Usage

size.ci.condmean(alpha, evar, xvar, diff, w)

Arguments

alpha: alpha level for 1-alpha confidence
evar: planning value of within group (error) variance
xvar: variance of fixed predictor variable
diff: difference between x* and mean of x
w: desired confidence interval width

Value

Returns the required total sample size

References

Bonett DG (2021). Statistical Methods for Psychologists https://dgbonett.sites.ucsc.edu/.

Examples

size.ci.condmean(.05, 120, 125, 15, 5)
#>  Total sample size
#>                210

# Should return:
# Total sample size
#               210