Confidence interval for a linear contrast of medians in a between-subjects design

Source: R/statpsych1.R

Computes a distribution-free confidence interval for a linear contrast of medians in a between-subjects design using estimated medians and their standard errors. The sample median and standard error for each group can be computed using the ci.median) function.

ci.lc.median.bs(alpha, m, se, v)

Arguments

alpha

alpha level for 1-alpha confidence

m

vector of estimated group medians

se

vector of group standard errors

v

vector of between-subjects contrast coefficients

Value

Returns a 1-row matrix. The columns are:

  • Estimate - estimated linear contrast of medians

  • SE - standard error

  • LL - lower limit of the confidence interval

  • UL - upper limit of the confidence interval

References

Bonett DG, Price RM (2002). “Statistical inference for a linear function of medians: Confidence intervals, hypothesis testing, and sample size requirements.” Psychological Methods, 7(3), 370--383. ISSN 1939-1463, doi:10.1037/1082-989X.7.3.370 .

Examples

m <- c(46.13, 29.19, 30.32, 49.15)
se <- c(6.361, 5.892, 4.887, 6.103)
v <- c(1, -1, -1, 1)
ci.lc.median.bs(.05, m, se, v)
#>  Estimate       SE       LL       UL
#>     35.77 11.67507 12.88727 58.65273

# Should return:
# Estimate       SE       LL       UL
#    35.77 11.67507 12.88727 58.65273