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Table 3 Final adjusted and trimmed model for headache days per montha

From: Fluctuations in episodic and chronic migraine status over the course of 1 year: implications for diagnosis, treatment and clinical trial design

Random-Effect Variance Parameter Estimates
  Estimate Standard Error  
 Intercept 0.52 0.01  
 Linear trend 0.15 0.01  
 Quadratic trend 0.09 0.01  
 Scale 0.08 0.005  
Fixed Effects b
 Label RR (95% CI) c DF t P value
 Intercept 1.16 (1.02–1.32) 16,650 2.28 0.0224
 Sex: male vs. female 0.9 (0.87–0.93) 16,650 6.62 <0.0001
 Education: college graduate vs. non–college graduate 0.96 (0.93–0.99) 16,650 2.92 0.0035
 Race: Caucasian vs. nonwhite 1.19 (1.14–1.23) 16,650 8.78 <0.0001
 Household income: at or above national median vs. those below 0.96 (0.94–0.99) 16,650 2.42 0.0155
 Comorbid count 1.07 (1.05–1.09) 16,650 8.06 <0.0001
 Disability: MIDAS category TIC 1.47 (1.46–1.49) 16,650 73.56 <0.0001
 Age at onset, y 0.998 (0.997–0.999) 16,650 3.20 0.0014
 Duration of illness 1.00 (1.001.00) 16,650 0.83 0.4090
 Linear trend 0.74 (0.73–0.76) 29,304 28.63 <0.0001
 Quadratic trend 1.09 (1.07–1.11) 29,304 8.35 <0.0001
 Cubic trend 0.99 (0.971.01) 29,304 1.34 0.1797
 Headache status: CM vs. EM 3.95 (3.84–4.07) 29,304 90.71 <0.0001
 Headache status by linear trend interaction 1.26 (1.2–1.33) 29,304 9.34 <0.0001
 Headache status by quadratic trend interaction 0.99 (0.941.03) 29,304 0.51 0.6434
 Headache status by cubic trend interaction 1.00 (0.961.04) 29,304 0.17 0.8627
  1. CM chronic migraine, DF degrees of freedom, EM episodic migraine, MIDAS Migraine Disability Assessment questionnaire, RR rate ratio, t t-statistic; TIC time invariant covariate, TVC time-varying covariate
  2. aIn persons with EM and CM and adjusting for demographic variables, headache related disability and comorbidity
  3. bAll covariates were specified as TICs, though TVCs could have been specified for several including MIDAS and comorbidity count, which may not have been constant over time
  4. cStatistically significant RR are bolded