Table 3.

Analyses* of the potential synergistic effects of the two exposures perceived work ability (PWA) and daily smoking (DS) on a favourable prognosis of long-duration activity-limiting neck and/or back pain

Exposure	Cases/total	Crude (n=3312)		Adjusted† (n=3049)
		RR	95% CI	RR	95% CI
Moderate/poor perceived work ability and daily smoking	39/253	1		1
Moderate/poor perceived work ability and no daily smoking	276/1022	1.88	1.32 to 2.66	1.61	1.11 to 2.34
Good perceived work ability and daily smoking	76/206	2.96	1.93 to 4.54	2.33	1.49 to 3.66
Good perceived work ability and no daily smoking	794/1811	3.96	2.84 to 5.52	2.80	1.95 to 4.02
Synergy index				0.92	0.60 to 1.43

*Using EpiNET’s epidemiological tool ‘Epinetcaculation.xlsx’ based on the results from logistic regressions.

†Adjusted for socioeconomic status, headache/migraine, sleep disturbances and subsample participation.

RR, risk ratio.