What works best for whom? An exploratory, subgroup analysis in a randomized, controlled trial on the effectiveness of a workplace intervention in low back pain patients on return to work.
METHODS
Exploratory subgroup analysis in a randomized controlled trial (RCT).


OBJECTIVE
To detect possible moderators in the effectiveness of a workplace intervention in a population of workers with sick leave due to sub acute nonspecific low back pain.


BACKGROUND
In a recently published RCT, a workplace intervention was effective on return to work, compared to usual care. Examining the heterogeneity of effect sizes within the population in this RCT (n = 196) can lead to information on the effectiveness of the intervention in subgroups of patients.


METHODS
A subgroup analysis was performed by adding interaction terms to the statistical model. Before analysis the following possible moderators for treatment were identified: age, gender, pain, functional status, heavy work, and sick leave in the previous 12 months. Cox regression analyses were performed and survival curves were plotted.


RESULTS
The interaction (P = 0.02) between age (dichotomized at the median value) and the workplace intervention indicates a modifying effect. The workplace intervention is more effective for workers > or =44 years (HR, 95% CI = 2.5, [1.6, 4.1] vs. 1.2 [0.8, 1.8] for workers <44 years old). The interaction between sick leave in the previous 12 months and the workplace intervention is significant (P = 0.02). The intervention is more effective for workers with previous sick leave (HR, 95% CI = 2.8 [1.7, 4.9] vs. 1.3 [0.8, 2.0]). A modifying effect of gender, heavy work, and pain score and functional status on the effectiveness of this intervention was not found.


CONCLUSIONS
The findings from these exploratory analyses should be tested in future RCTs. This workplace intervention seems very suitable for return to work of older workers and workers with previous sick leave. Gender, perceived heavy work, and baseline scores in pain and functional status should not be a basis for assignment to this intervention.
Institute for Work and Health, Toronto, Canada.
Ivan A
IA
Steenstra
Dirk L
DL
Knol
Paulien M
PM
Bongers
Johannes R
JR
Anema
Willem
W
van Mechelen
Henrica C W
HC
de Vet
D000203:Activities of Daily Living; D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D015331:Cohort Studies; D004185:Disability Evaluation; D006804:Ergonomics / Q000379:methods; D005260:Female; D006293:Health Promotion / Q000379:methods; D006801:Humans; D017116:Low Back Pain / Q000453:epidemiology* / Q000517:prevention & control / Q000534:rehabilitation*; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases; D016273:Occupational Exposure / Q000009:adverse effects / Q000706:statistics & numerical data; D016272:Occupational Health / Q000706:statistics & numerical data; D017063:Outcome Assessment, Health Care / Q000379:methods; D010147:Pain Measurement; D016730:Program Development / Q000379:methods; D012737:Sex Factors; D018582:Sick Leave / Q000706:statistics & numerical data*; D016037:Single-Blind Method; D014938:Work Capacity Evaluation; D014940:Work Schedule Tolerance; D017132:Workplace / Q000706:statistics & numerical data; D055815:Young Adult