replicate.mean2 {vcmeta}

Compares and combines 2-group mean differences in original and follow-up studies

Description

This function computes confidence intervals from an original study and a follow-up study where the effect size is a 2-group mean difference. Confidence intervals for the difference and average effect size are also computed. Equality of variances within or across studies is not assumed. A Satterthwaite adjustment to the degrees of freedom is used to improve the accuracy of the confidence intervals. The same results can be obtained using the meta.lc.mean2 function with appropriate contrast coefficients. The confidence level for the difference is 1 – 2*alpha, which is recommended for equivalence testing.

Usage

replicate.mean2(
  alpha,
  m11,
  m12,
  sd11,
  sd12,
  n11,
  n12,
  m21,
  m22,
  sd21,
  sd22,
  n21,
  n22
)

Arguments

alpha

alpha level for 1-alpha confidence

m11

estimated mean for group 1 in original study

m12

estimated mean for group 2 in original study

sd11

estimated SD for group 1 in original study

sd12

estimated SD for group 2 in original study

n11

sample size for group 1 in original study

n12

sample size for group 2 in original study

m21

estimated mean for group 1 in follow-up study

m22

estimated mean for group 2 in follow-up study

sd21

estimated SD for group 1 in follow-up study

sd22

estimated SD for group 2 in follow-up study

n21

sample size for group 1 in follow-up study

n22

sample size for group 2 in follow-up study

Value

A 4-row matrix. The rows are:

• Row 1 summarizes the original study

• Row 2 summarizes the follow-up study

• Row 3 estimates the difference in mean differences

• Row 4 estimates the average mean difference

The columns are:

• Estimate - mean difference estimate (single study, difference, average)

• SE - standard error

• t - t-value

• p - p-value

• LL - lower limit of the confidence interval

• UL - upper limit of the confidence interval

• df - degrees of freedom

References

Bonett DG (2021). “Design and analysis of replication studies.” Organizational Research Methods, 24(3), 513–529. ISSN 1094-4281, doi:10.1177/1094428120911088.

Examples

replicate.mean2(.05, 21.9, 16.1, 3.82, 3.21, 40, 40, 
                     25.2, 19.1, 3.98, 3.79, 75, 75)

# Should return:
#                     Estimate        SE          t            p 
# Original:               5.80 0.7889312  7.3517180 1.927969e-10  
# Follow-up:              6.10 0.6346075  9.6122408 0.000000e+00  
# Original - Follow-up:  -0.30 1.0124916 -0.2962988 7.673654e-01 
# Average:                5.95 0.5062458 11.7531843 0.000000e+00 
#                               LL       UL        df
# Original:               4.228624 7.371376  75.75255
# Follow-up:              4.845913 7.354087 147.64728
# Original - Follow-up:  -1.974571 1.374571 169.16137
# Average:                4.950627 6.949373 169.16137