Computes an approximate one-sided or two-sided prediction interval for the estimated proportion in a future study with a planned sample size of n. The prediction interval uses a proportion estimate from a prior study that had a sample size of n0.
Several confidence interval sample size functions in this package require a planning value of the expected sample value of a proportion in the planned study. A one-sided proportion prediction limit is useful as a proportion planning value for a conservatively large sample size required to obtain a confidence interval with desired width. This strategy for specifying a proportion planning value is useful in applications where the population proportion in the prior study is assumed to be very similar to the population proportion in the planned study.
For sample size planning, use an upper prediction limit if the population proportion is assumed to be less than .5; and if the upper prediction limit is greater than .5, set the proportion planning value to .5. Use a lower prediction limit if the population proportion is asumed to be greater than .5; and if the lower prediction limit is less than .5, set the proportion planning value to .5.
For more details, see Section 1.16 of Bonett (2021, Volume 3)
Arguments
- alpha
alpha value for 1-alpha confidence
- prop
estimated proportion from prior study
- n0
sample size used to estimate proportion in prior study
- n
planned sample size of future study
- type
set to 1 for two-sided prediction interval
set to 2 for one-sided upper prediction limit
set to 3 for one-sided lower prediction limit
Value
Returns one-sided or two-sided prediction limit(s) for an estimated proportion in a future study