ci.lc.prop.scheffe: Scheffe confidence interval for a linear contrast of...

In statpsych: Statistical Methods for Psychologists

Scheffe confidence interval for a linear contrast of proportions in a between-subjects design

Description

Computes an adjusted Wald confidence interval for a linear contrast of population proportions in a between-subjects design using a Scheffe critical value. A Scheffe p-value is computed for the test statistic. This function is useful in exploratory studies where the linear contrast of proportions was not planned but was suggested by the pattern of sample proportions. Use the ci.lc.prop.bs function with a Bonferroni adjusted alpha value to compute simultaneous confidence intervals for two or more planned linear contrasts of proportions.

For more details, see Section 2.9 of Bonett (2021, Volume 3)

Usage

ci.lc.prop.scheffe(alpha, f, n, v)

Arguments

alpha	alpha level for 1-alpha confidence
f	vector of frequency counts of participants who have the attribute
n	vector of sample sizes
v	vector of between-subjects contrast coefficients

Value

Returns a 1-row matrix. The columns are:

• Estimate - adjusted estimate of proportion linear contrast

• SE - adjusted standard error

• z - z test statistic

• p - two-sided Scheffe p-value

• LL - lower limit of the Scheffe confidence interval

• UL - upper limit of the Scheffe confidence interval

References

\insertRef

Price2004statpsych

\insertRef

Marascuilo1977statpsych

\insertRef

Bonett2021statpsych

Examples

f <- c(26, 24, 38)
n <- c(60, 60, 60)
v <- c(-.5, -.5, 1)
ci.lc.prop.scheffe(.05, f, n, v)

# Should return:
#  Estimate         SE      z       p         LL        UL
# 0.2119565 0.07602892 2.7878 0.02053 0.02585698 0.3980561

statpsych documentation built on Jan. 13, 2026, 1:07 a.m.