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Table 2 Unadjusted model for headache days per month for persons with EM and CM

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 0.82 0.01  
Linear trend 0.17 0.01  
Quadratic trend 0.09 0.01  
Scale 0.09 0.005  
Fixed Effects
Label RR (95% CI) a DF t P value
Intercept 3.98 (3.82–4.15) 16,788 66.53 <0.0001
Linear trend 0.73 (0.72–0.75) 29,528 28.49 <0.0001
Quadratic trend 1.09 (1.06–1.11) 29,528 7.90 <0.0001
Cubic trend 0.98 (0.971.00) 29,528 1.51 0.1318
Headache status: CM vs. EM 4.45 (4.3–4.59) 29,528 89.36 <0.0001
Headache status by linear trend interaction 1.19 (1.13–1.26) 29,528 6.67 <0.0001
Headache status by quadratic trend interaction 1.03 (0.981.08) 29,528 1.26 0.2075
Headache status by cubic trend interaction 0.99 (0.951.03) 29,528 0.72 0.4710
  1. CM chronic migraine, DF degrees of freedom, EM episodic migraine, RR rate ratio, t t-statistic
  2. aStatistically significant RRs are bolded