ci.stdmean2 {statpsych}

Confidence interval for a 2-group standardized mean difference

Description

Computes confidence intervals for a population standardized mean difference. Unweighted, weighted, and single group variance standardizers are used. The square root weighted variance standardizer is recommended in 2-group nonexperimental designs with simple random sampling. The square root unweighted variance standardizer is recommended in 2-group experimental designs. The single group standard deviation standardizer can be used with experimental or nonexperimental designs. Equality of variances is not assumed.

Usage

ci.stdmean2(alpha, m1, m2, sd1, sd2, n1, n2)

Arguments

alpha

alpha level for 1-alpha confidence

m1

estimated mean for group 1

m2

estimated mean for group 2

sd1

estimated standard deviation for group 1

sd2

estimated standard deviation for group 2

n1

sample size for group 1

n2

sample size for group 2

Value

Returns a 4-row matrix. The columns are:

• Estimate - estimated standardized mean difference

• adj Estimate - bias adjusted standardized mean difference estimate

• SE - standard error

• LL - lower limit of the confidence interval

• UL - upper limit of the confidence interval

References

Bonett DG (2008). “Confidence intervals for standardized linear contrasts of means.” Psychological Methods, 13(2), 99–109. ISSN 1939-1463, doi:10.1037/1082-989X.13.2.99.

Examples

ci.stdmean2(.05, 35.1, 26.7, 7.32, 6.98, 30, 30)

# Should return:
#                          Estimate  adj Estimate        SE        LL       UL
# Unweighted standardizer: 1.174493      1.159240 0.2844012 0.6170771 1.731909
# Weighted standardizer:   1.174493      1.159240 0.2802826 0.6251494 1.723837
# Group 1 standardizer:    1.147541      1.117605 0.2975582 0.5643375 1.730744
# Group 2 standardizer:    1.203438      1.172044 0.3120525 0.5918268 1.815050