Table 5

Results from multivariate linear regression analyses of cost drivers

	RA		AS		PsA		SLE
	Coeff	95% CI	Coeff	95% CI	Coeff	95% CI	Coeff	95% CI
AS, ankylosing spondylitis; Coeff, coefficient; FCA, friction cost approach; HCA, human capital approach; NI, not included; PsA, psoriatic arthritis; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus.
Direct costs
Positive rheumatoid factor	825	377 to 1273	NI		NI		NI
Steinbrocker’s functional class (per unit)	1185	848 to 1522	NI		NI		NI
Disease activity (per unit, 0–10)	336	214 to 458	207	10 to 403	387	211 to 563	506	291 to 721
Function (per unit of worsening; 100–0)	72	62 to 82	19	0.3 to 39	46	31 to 61	34	12 to 55
Disease duration (per year)							−65	−188 to −11
Years of education (per year)	234	82 to 387
Indirect costs (HCA)
Male sex	3014	1866 to 4163	2896	797 to 4994
Positive rheumatoid factor	1328	320 to 2336	NI		NI		NI
Steinbrocker’s functional class (per unit)	2332	1600 to 3065			NI		NI
Function (per unit of worsening; 100–0)	236	214 to 258	285	233 to 337	320	277 to 365	346	285 to 407
Disease duration (per year)	257	200 to 313	164	60 to 269	356	232 to 479	420	269 to 570
Age (per year)	111	61 to 160	249	149 to 349			118	15 to 222
Age at disease onset (per year)					130	42 to 218
Years of education (per year)			−1384	−2235 to −533
Total costs (HCA)
Male sex	2995	1711 to 4279	2906	594 to 5218
Positive rheumatoid factor	2295	1168 to 3422	NI		NI		NI
Steinbrocker’s functional class (per unit)	3844	3024 to4663	NI		NI		NI
Disease activity (per unit, 0–10)							902	244 to 1560
Function (per unit of worsening, 100–0)	314	289 to 338	317	259 to 375	379	331 to 426	370	300 to 441
Disease duration (per year)	253	189 to 317			322	187 to 458	353	184 to 522
Age (per year)	93	38 to 148	366	245 to 486			123	5 to 241
Age at disease onset (per year)			−137	−253 to −22	100	4 to 196
Years of education (per year)			−1266	−2203 to−328