Table 3 Ordinal logistic regression for association between socioeconomic status (SES) and headache impact (HIT-6). Addition of interaction “SES * obesity” to Model 4. Weighted random sample

SES (ref. = high)

 Low SES

.296

.277

-0.25, 0.84

 Medium SES

.158

.209

-0.25, 0.57

Other Sociodemographic variables

 Sex (ref. = men)

.581***

.157

0.27, 0.89

 Age

-.004

.007

-0.02, 0.01

 Marital status (ref. = married)

  Unmarried

.125

.259

-0.38, 0.63

  Divorced

-.038

.279

-0.59, 0.51

  Widowed

-.491

.366

-1.21, 0.23

Living without partner (ref. = living with partner)

-.089

.238

-0.56, 0.38

Children < 18 years (ref. = no)

.079

.191

-0.30. 0.45

Living in a rural area (ref. = living in an urban area)

.153

.214

-0.27, 0.57

Headache-related variables

 Analgesic use (days a month)

.087***

.016

0.06, 0.12

 Headache frequency (ref. = less than 4 days a month)

  4–14 days a month

1.222***

.210

0.81, 1.63

  > 14 days a month

.485

.455

-0.41, 1.38

 Migraine (ref. = no)

1.473***

.182

1.12, 1.83

Other health variables

 Physical inactivity (ref. = physical active persons)

.242

.159

-0.07, 0.55

 Obesity (BMI ≥ 30) (ref. = no obesity)

-.368

.431

-1.21, 0.48

 Depressive symptoms (PHQ) (ref. = no depressive symptoms)

.650**

.234

0.19, 1.11

Interaction

 SES * Obesity

  Low SES: obesity (ref. = no obesity)

1.292*

.577

0.16, 2.42

  Medium SES: obesity (ref. = no obesity)

.462

.487

-0.49, 1.42

 Model fitting: χ² (df)

277.83 (20) ***

 Goodness of fit

  (Pearson) χ² (df)

2202.79 (2248)

  (Deviance) χ² (df)

1647.66.73 (2248)

Pseudo-R² (Nagelkerke`s)

.341

Test of proportional odds: χ² (df)

47.00(40)