Distinguishing fibromyalgia from rheumatoid arthritis and systemic lupus in clinical questionnaires: an analysis of the revised Fibromyalgia Impact Questionnaire (FIQR) and its variant, the Symptom Impact Questionnaire (SIQR), along with pain locations

Table 4 Stepwise multiple regression showing 15 predictors ranked in order of magnitude in predicting group membership (FM or RA/SLE)

Predictors	Step and number of variables included	Multiple R	Multiple R²	R² change	Pvalue for predictor variable
Mid-lower back	1	0.540	0.291	0.291	0.00000
Tenderness to touch	2	0.637	0.406	0.115	0.00000
Neck	3	0.689	0.474	0.068	0.00000
Arms	4	0.712	0.507	0.033	0.00007
Hands	5	0.747	0.558	0.051	0.00000
Lateral lower back	6	0.758	0.575	0.017	0.00168
Sitting for 45 minutes	7	0.768	0.589	0.014	0.00367
Feeling overwhelmed	8	0.775	0.601	0.012	0.00750
Depression	9	0.784	0.615	0.014	0.00365
Sensitivity	10	0.791	0.626	0.011	0.00855
Thighs	11	0.797	0.635	0.009	0.01471
Feet	12	0.804	0.647	0.012	0.00529
Cleaning floors	13	0.806	0.649	0.003	0.16326
Anxiety	14	0.807	0.652	0.002	0.19893
Memory	15	0.809	0.654	0.002	0.21899

Note: This forward stepwise regression analysis used 15 predictors which combined to produce a multiple R = 0.809 (last row, column 2). This accounted for 65% of variance associated with group membership (column 3). FM, fibromyalgia; RA/SLE, combined rheumatoid arthritis and systemic lupus erythematosus group.

ISSN: 1478-6362