ci.prop2.inv {statpsych}

Confidence interval for a 2-group proportion difference using inverse sampling

Description

Computes an approximate confidence interval for a population proportion difference when inverse sampling has been used. An approximate standard error is recovered from the confidence interval. With inverse sampling, the number of participants who have the attribute within group 1 (f1) and group 2 (f2) are predetermined, and sampling continues within each group until f1 and f2 attain their prespecified values. With inverse sampling, the sample sizes (n1 and n2) will not be known in advance.

Usage

ci.prop2.inv(alpha, f1, f2, n1, n2)

Arguments

alpha

alpha level for 1-alpha confidence

f1

number of participants in group 1 who have the attribute (fixed)

f2

number of participants in group 2 who have the attribute (fixed)

n1

sample size for group 1 (random)

n2

sample size for group 2 (random)

Value

Returns a 1-row matrix. The columns are:

• Estimate - estimate of proportion difference

• SE - recovered standard error

• LL - lower limit of confidence interval

• UL - upper limit of confidence interval

References

Zou GY (2010). “Confidence interval estimation under inverse sampling.” Computational Statistics & Data Analysis, 54(1), 55–64. ISSN 0167-9473, doi:10.1016/j.csda.2005.05.007.

Examples

ci.prop2.inv(.05, 10, 10, 48, 213)

# Should return:
#  Estimate         SE         LL        UL
#  0.161385 0.05997618 0.05288277 0.2879851