Group statistics from Jordaan's (2014) study with three posttest occasions

The sample sizes, means, and standard deviations of a Solomon four-group design measured on three posttest occasions: an evaluation of a life skills program for young adult male offenders (Jordaan, 2014, Table 7.3, p. 112). The outcomes are the three subscales of the Coping Strategy Indicator. Numbers reported in the publication are reused with citation.

Usage

jordaan2014

Format

A data frame with 42 rows, one per subscale, group, and occasion, and 8 variables:

subscale: Social support, Problem solving, or Avoidance.
group: The group's number in the thesis: 1 = program with pretest, 2 = program without pretest, 3 = control with pretest, 4 = control without pretest.
treat: 1 for the program groups, 0 for the control groups.
pretested: 1 if the group was pretested, 0 if not.
occasion: Pretest (groups 1 and 3 only), Posttest (after the program), Follow-up 1 (3 months later), or Follow-up 2 (6 months later).
n: Sample size.
mean, sd: Mean and standard deviation.

Source

Jordaan, J. (2014). The development and evaluation of a life skills programme for young adult prisoners [Doctoral thesis, University of the Free State]. KovsieScholar. https://hdl.handle.net/11660/832

Details

Design. 120 offenders aged 21 to 25 with long sentences were selected by systematic random sampling in a maximum-security correctional center and assigned at random to the program or the control condition. Half of each condition was assigned at random to be pretested (pp. 86–87). The program ran for six months; the control group followed the center's normal daily activities (p. 87). All groups were tested after the program and again 3 and 6 months later (p. 98).

Attrition. Transfers removed 17 offenders from the program groups and 7 from the control groups, leaving 96 (p. 109). Those 96 completed every posttest: every analysis in the thesis has 92 error degrees of freedom. Because more were lost from the program groups, the groups analyzed are not guaranteed to be comparable, even though they were randomized.

Measures. Each subscale of the Coping Strategy Indicator has 11 items scored from 1 (not at all) to 3 (a lot), so scores range from 11 to 33. High scores on problem solving and on seeking social support, and low scores on avoidance, indicate better coping (p. 92).

Known results. These statistics reproduce, within rounding, the 2 x 2 analyses of variance of the posttests on each occasion (Tables 7.4–7.19, pp. 113–127). The Pretest x Treatment interaction F values are:

Social support: 9.678 (p = .002) after the program, 0.266 at 3 months, and 2.306 at 6 months.
Problem solving: 0.819, 0.563, and 5.556 (p = .021).
Avoidance: 0.373, 0.688, and 0.327.

The thesis followed the decision sequence of Walton Braver and Braver (1988) on each occasion separately (fit_solomon_classic()). The correlations between occasions are not reported, so analyses of change across occasions cannot be reproduced; see the article "Worked Example: Repeated Posttests".

References

Walton Braver, M. C., & Braver, S. L. (1988). Statistical treatment of the Solomon four-group design: A meta-analytic approach. Psychological Bulletin, 104(1), 150–154. https://doi.org/10.1037/0033-2909.104.1.150

Examples

# Problem solving, 6 months after the program (Table 7.13, p. 121).
ps6 <- subset(jordaan2014, subscale == "Problem solving" & occasion == "Follow-up 2")
with(ps6, solomon_from_summary(n, mean, sd, treat = treat, pretested = pretested))
#> Solomon analysis from summary statistics
#> ----------------------------------------
#> Pooled error variance: 11.657 on 92 df (equal variances assumed)
#> 
#> Two-way ANOVA on the posttest (Type III sums of squares)
#>   Treatment            SS =    0.115  df = 1  F = 0.01  p = 0.921
#>   Pretest              SS =    0.059  df = 1  F = 0.01  p = 0.944
#>   Treatment x Pretest  SS =   64.539  df = 1  F = 5.54  p = 0.021
#>   Error                SS = 1072.442  df = 92
#> 
#> Contrasts with 95% confidence intervals
#>   Test A: Pretest x Treatment               3.320 [0.518, 6.122], t(92) = 2.35, p = 0.021
#>   Test B: Treatment | pretested             1.590 [-0.455, 3.635], t(92) = 1.54, p = 0.126
#>   Test C: Treatment | unpretested          -1.730 [-3.646, 0.186], t(92) = -1.79, p = 0.076
#>   Test D: ATE (avg over pretest)           -0.070 [-1.471, 1.331], t(92) = -0.10, p = 0.921
#>   Pretest main effect                      -0.050 [-1.451, 1.351], t(92) = -0.07, p = 0.944