Table 5. Confirmatory One-Factor, Two-Factor, and Bi-factor Model Statistics for the PHQ-ADS *.
| Fit Index | SCOPE Trial (n = 250) | ESCAPE Trial (n = 241) | INCPAD Trial (n = 405) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| 1-factor | 2-factor | Bi-factor | 1-factor | 2-factor | Bi-factor | 1-factor | 2-factor | Bi-factor | |
| Number of parameters | 64 | 65 | 80 | 64 | 65 | 80 | 64 | 65 | 80 |
| Chi-square (df) | 318.0 (104) | 290.6 (103) | 250.39 (88) | 278.7 (104) | 228.0 (103) | 167.1 (88) | 817.7 (104) | 407.1 (103) | 161.6 (88) |
| RMSEA | .091 | .085 | .086 | .083 | .071 | .061 | .130 | .085 | .045 |
| CFI | 0.956 | 0.962 | 0.967 | 0.954 | 0.967 | 0.979 | 0.862 | .941 | .986 |
| WRMR | 1.179 | 1.110 | 0.949 | 1.114 | 0.981 | 0.755 | 2.040 | 1.384 | 0.740 |
| Estimated factor correlations | n/a | 0.912 | † | n/a | 0.865 | † | n/a | 0.653 | † |
| Explained common variance | 0.854 | 0.792 | 0.634 | ||||||
| Omega hierarchical index | 0.906 | 0.891 | 0.743 | ||||||
| Correlation between 1-factor model loadings and general factor loadings from bi-factor model | 0.97 | 0.73 | 0.79 | ||||||
*
Strict unidimensional model fit was evaluated using absolute (i.e., chi square), parsimony-adjusted RMSEA (i.e., root mean square error of approximation; cutoff ≤ .06), incremental CFA fit indices (i.e., comparative fit index; cutoff ≥ .95), and WRMR fit indices (i.e., weighted root mean square residual, cutoff ≤ 1.0) Sufficient unidimensionality in the bi-factor model was evidenced by: explained common variance greater than 0.60, omega hierarchical index greater than 0.70, and a high correlation (e.g. r >.90) between the factor loadings of the unidimensional model and the general factor of the bi-factor model.
†
Each pair constrained to zero