statpsych (version 2.0.0)

size.ci.cor.prior: Sample size for a Pearson correlation confidence interval using an estimated correlation from a prior study

Description

Computes the sample size required to estimate a Pearson correlation with desired confidence interval precision in applications where an estimated Pearson correlation from a prior study is available. The actual confidence interval width in the planned study will depend on the value of the estimated correlation in the planned study. An estimated correlation from a prior study can be used to compute a prediction interval for the value of the estimated correlation in the planned study, which is then used as a planning value in the sample size analysis. If the prediction interval includes 0, then the correlation planning value is set to 0; otherwise, the correlation planning value is set to the lower prediction limit (if the prior correlation is positive) or the upper prediction limit (if the prior correlation is negative). The probability that the 1 - alpha1 confidence interval in the planned study will have a width that is less than the desired width is approximately 1 - alpha2 where alpha1 and alpha2 are specified values.

This sample size approach assumes that the population Pearson correlation that was estimated in the prior study is very similar to the population Pearson correlation that will be estimated in the planned study. If an estimated Pearson correlation from a prior study is not available the researcher must use expert opinion to guess the value of the Pearson correlation that will be observed in the planned study. The size.ci.cor function uses a correlation planning value that is based on expert opinion regarding the likely value of the correlation estimate that will be observed in the planned study.

For more details, see Section 1.26 of Bonett (2021, Volume 2)

Usage

size.ci.cor.prior(alpha1, alpha2, cor0, n0, w)

Value

Returns the required sample size

Arguments

alpha1

alpha level for 1-alpha1 confidence in the planned study

alpha2

alpha level for the 1-alpha2 prediction interval

cor0

estimated correlation in prior study

n0

sample size in prior study

w

desired confidence interval width

References

Bonett2021statpsych

Examples

size.ci.cor.prior(.05, .10, -.56, 120, .2)

# Should return:
# Sample size
#         246