Table 3.

Sensitivity Analysis of Incidence Rates per 100,000 person-years (2004–2008)

	Commercial and Medicare supplemental database				Medicaid database
	N	Crude rate	Age & Gender adjusted rate	95% CI for adjusted rate	N	Crude rate	Age & Gender adjusted rate	95% CI for adjusted rate
Base case analysis (IIMs)	2,477	4.88	4.27	4.09-4.44	513	5.20	5.23	4.74-5.72
Dermatomyositis	902	1.78	1.52	1.42-1.63	170	1.72	1.70	1.42-1.97
Polymyositis	1,438	2.83	2.46	2.33-2.59	346	3.51	3.53	3.13-3.94
Interstitial myositis	401	0.79	0.73	0.66-0.81	75	0.76	0.78	0.58-0.97
Presence of muscle biopsy one year prior to or one year following index date
IIMs	738	1.45	1.25	1.16-1.35	102	1.03	1.05	0.83-1.27
Dermatomyositis	248	0.49	0.43	0.38-0.49	34	0.34	0.34	0.22-0.46
Polymyositis	574	1.13	0.96	0.88-1.04	88	0.89	0.91	0.70-1.11
Interstitial myositis	21	0.04	0.04	0.02-0.06	2	0.02	0.02	0.01-0.04
Presence of specialist visit on index date or in the year following
IIMs	535	1.05	0.91	0.82-0.99	64	0.65	0.63	0.46-0.79
Dermatomyositis	207	0.41	0.35	0.30-0.40	21	0.21	0.24	0.13-0.35
Polymyositis	374	0.74	0.63	0.56-0.70	49	0.50	0.46	0.32-0.59
Interstitial myositis	27	0.05	0.05	0.03-0.07	8	0.08	0.06	0.02-0.10
Presence of immunosuppressants and/or systemic corticosteroids one year following index date
IIMs	1,761	3.47	3.01	2.86-3.16	304	3.08	3.07	2.70-3.44
Dermatomyositis	725	1.43	1.24	1.14-1.33	103	1.04	1.02	0.80-1.23
Polymyositis	1,146	2.26	1.96	1.84-2.08	225	2.28	2.29	1.97-2.61
Interstitial myositis	133	0.26	0.23	0.19-0.27	32	0.32	0.31	0.20-0.43
Presence of any of the above (combined sensitivity criteria)
IIMs	1,917	3.78	3.29	3.13-3.44	347	3.52	3.50	3.10-3.89
Dermatomyositis	758	1.49	1.29	1.20-1.39	115	1.17	1.13	0.91-1.36
Polymyositis	1,250	2.46	2.14	2.01-2.26	257	2.61	2.62	2.28-2.97
Interstitial myositis	160	0.32	0.28	0.24-0.33	38	0.38	0.36	0.24-0.48