Table 4.
Results of two-group item response theory analysis
| Symptom | Constrained parameter | No. of free parameters | Log-likelihood | Δχ2 | df | P | Sample size- adjusted BIC |
| Base model | – | 31 | −6,922.92 | – | – | – | 13,965.44 |
| Withdrawal | Loading | 30 | −6,923.69 | 1.60 | 1 | .2060 | 13,962.13 |
| Threshold | 30 | −6,928.01 | 11.65 | 1 | .0006* | 13,968.13 | |
| Caused problems | Loading | 30 | −6,923.63 | 1.31 | 1 | .2521 | 13,961.99 |
| Threshold | 30 | −6,938.48 | 24.05 | 1 | <.0001* | 13,997.66 | |
| Role failure | Loading | 30 | −6,923.04 | 0.20 | 1 | .6578 | 13,963.86 |
| Threshold | 30 | −6,929.87 | 13.98 | 1 | .0002* | 13,979.96 | |
| Hazardous use | Loading | 30 | −6,926.58 | 5.65 | 1 | .0174 | 13,965.06 |
| Threshold | 30 | −6,935.48 | 26.88 | 1 | <.0001* | 13,990.00 | |
| Social problems | Loading | 30 | −6,924.02 | 2.15 | 1 | .1424 | 13,962.21 |
| Threshold | 30 | −6,925.89 | 7.56 | 1 | .0059* | 13,969.93 | |
| Final model- All factor loadings constrained | 26 | −6,929.00 | 11.52 | 5 | .0420 | 13,958.30 |
Notes: BIC = Bayesian information criterion; bolded text indicates best-fitting model.
*
Indicates significant result at p < .01.