Multivariable analysis exploring determinants of employment in patients aged≤65 years stratified by level of education
| Variable | AS—low education (n=145)BASDAI model | AS—high education (n=68)BASDAI model | AS—low education (n=145)BASFI model | AS—high education (n=68)BASFI model | ||||||||
| IRR | CI | P values | IRR | CI | P values | IRR | CI | P values | IRR | CI | P values | |
| Age, years | 0.98 | 0.97 to 0.99 | <0.01 | 0.99 | 0.98 to 1.01 | 0.21 | 0.98 | 0.97 to 0.99 | <0.01 | 0.99 | 0.98 to 1.01 | 0.51 |
| Gender, male | 1.27 | 0.94 to 1.70 | 0.12 | 1.01 | 0.73 to 1.40 | 0.94 | 1.26 | 0.95 to 1.67 | 0.11 | 0.95 | 0.72 to 1.27 | 0.74 |
| BMI, kg/m2 | * | * | * | * | ||||||||
| Smoking, current | * | * | * | * | ||||||||
| Alcohol use, current | † | † | † | † | ||||||||
| Comorbidity (SCQ, 0–39) | † | † | † | † | ||||||||
| Presence of any EAM, yes | * | † | * | † | ||||||||
| Symptom duration, years | † | * | † | * | ||||||||
| BASDAI (0–10) | 0.97‡ | 0.91 to 1.04 | 0.39 | 0.98§ | 0.91 to 1.06 | 0.65 | ¶ | ¶ | ||||
| BASFI (0–10) | ¶ | ¶ | 0.95 | 0.89 to 1.01 | 0.07 | 0.94§ | 0.88 to 1.00 | 0.06 | ||||
| SF-36 MCS (0–100) | * | * | * | * | ||||||||
| Mastery (7–28) | 1.06 | 1.02 to 1.10 | <0.01 | † | 1.05 | 1.01 to 1.09 | <0.01 | † | ||||
Due to collinearity between BASDAI and BASFI, separate analyses were carried out using either BASDAI or BASFI.
Due to missing data, 213 (of 214) AS patients and 465 (of 470) controls were included in this analysis.
n/a: as the AS samples were stratified by education, education itself could not be included in the multivariable model as independent variable.
* Variable not tested in multivariable analysis, due to absence of association with outcome in univariable analysis (p≥0.20).
† Variable tested in multivariable analysis, but not significant and no confounder in multivariable analysis (therefore not included in model).
‡ BASDAI or BASFI was forced into the model despite not being significant (to allow for comparison of results across models).
§ Confounder.
¶ Variable not tested in multivariable analysis, due to collinearity with other variable (BASDAI or BASFI).
AS, ankylosing spondylitis; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; BMI, body mass index; EAM, extra-articular manifestation; IRR, incidence rate ratio; SCQ, Self-Administered Comorbidity Questionnaire; SF-36 MCS, Short-Form 36 Mental Component Summary.