Prediction model for unsuccessful return to work after hospital-based intervention in low back pain patients

Table 3 Multivariate logistic regression analyses resulting in 2 final prediction models

Variables	OR	95% CI	P
*One-year U-RTW, final prediction model, N=282*
Risk groups: Final combination variable Overall p			<0.001
(pain/side-flexion, bodily distress, 4 dichotomous variables²)
Low	1
Intermediate	5.04	2.11-12.02
High	15.5	6.56-36.41
Radiculopathy¹, ref. non-specific LBP	0.57	0.27-1.120	0.138
BMI in non-spec. LBP group, ref. 25 kg/m²	0.97	0.91-1.03	0.305
Effect modification BMI:
OR(BMI radiculopathy)/OR(BMI non-specific)	1.33	1.12-1.57	0.001
Age in non-spec. LBP group, ref. 40 years	0.99	0.96-1.03	0.589
Effect modification age:
OR(age radiculopathy)/ OR(age non-specific)	1.08	1.01-1.15	0.025
AUC 0.79.
Cut point 0.38: 71% correctly classified
*Initial U-RTW, final model, N=282*
Risk groups: Final combination variable Overall p			<0.001
(pain/side-flexion, bodily distress, 4 dichotomous variables²)
Low	1
Intermediate	3.23	1.24-8.40
High	7.94	3.20-19.7
Radiculopathy¹, ref. non-specific LBP	0.82	0.39-1.74	0.611
BMI in non-spec. LBP group, ref. 25 kg/m²	0.99	0.92-1.06	0.695
Effect modification BMI:
OR(BMI radiculopathy)/OR(BMI non-specific)	1.24	1.06-1.44	0.006
Age	1.03	1.00-1.06	0.082
AUC 0.73
Cut point 0.25: 66% correctly classified

The upper model with unsuccessful return to work at one year as outcome (one-year U-RTW).
The lower model with unsuccessful return to work during the year as outcome (initial U-RTW).
Adjustment for intervention group did not change the models. There was no effect modification for the final combination variable between patients with and without radiculopathy (one-year U-RTW, p=0.253, initial U-RTW, p=0.842).
¹ Interpreted as the difference of return to work in two patients with and without radiculopathy, both persons 40 years old with BMI 25 kg/m² and not different regarding other risk factors.
² Final combination variable of pain/side-flexion (3 groups), bodily distress (4 groups) and 4 dichotomous risk factors: ‘Not convinced about return to work within 6 months’, ‘blaming the work for pain’, ‘drinking alcohol less than once/month’, ‘no home owner ship’.
43 missing values in the combination model: Pain score (9), bodily distress (19), blaming the work for pain (7), home ownership (4), drinking alcohol less than once/month (3), BMI (1).
OR: Odds Ratio. CI: Confidence interval. AUC: Area under curve

ISSN: 1471-2474