Table 1. Descriptive Statistics for Characteristics of Studies Contributing Group Difference Effect Sizes (k = 73; n = 250).
| Mean | SD a | Range | |
|---|---|---|---|
| Method Characteristics | |||
| Publication year | 2001 | 5.8 | 1981 - 2008 |
| Conducted in the U.S. (1=yes) | .90 | .30 | 0 - 1 |
| Journal publication (1=yes) | .84 | .37 | 0 - 1 |
| Randomized design (1=yes) | .99 | .12 | 0 - 1 |
| Average attrition rate | .17 | .17 | 0 - .70 |
| Established survey instrument (1=yes)b | .61 | .49 | 0 - 1 |
| Time span of outcome measure (days)b | 64.9 | 45.3 | 28 - 267 |
| Pretest-posttest interval (days) b | 157.3 | 147.3 | 28 - 1456 |
| Effect size based on means/SDs (1=yes)b | .64 | .48 | 0 - 1 |
| Pretest group difference effect sizebc | .04 | .48 | −1.18 - 2.57 |
| Group equivalence effect sizec | .27 | .29 | −.40 - 1.23 |
| Participant Sample Characteristics | |||
| Percent male | 67.8 | 17.6 | 0 - 90 |
| Percent white | 60.8 | 26.9 | 0 - 100 |
| Age (years) | 16.5 | 1.56 | 14 - 20 |
| Clinical comorbidity (1=yes) | .47 | .50 | 0 - 1 |
| Substance severity factor score | 1.70 | .61 | 1 - 3 |
| Delinquency level/police contact | 2.55 | 1.32 | 1 - 5 |
| Referred from prior treatment (1=yes) | .32 | .47 | 0 - 1 |
| Treatment Characteristics | |||
| Delivered in group format (1=yes) | .32 | .47 | 0 - 1 |
| Level of family involvement | 1.57 | .64 | 1 - 3 |
| Implementation quality | .24 | .59 | −1.22 - 1.06 |
| Duration (days) | 76.4 | 67.5 | 1 - 380 |
| Frequency of treatment contact | 2.80 | 1.29 | 1 - 6 |
Note:
a
SD = standard deviation
b
Estimates calculated at the effect size level (n = 250); all others calculated for the k=73 group comparisons.
c
Mean estimates weighted using inverse variance weights.