Table 5 Ordinal logistic regression for association between socioeconomic status (SES) and headache impact (HIT-6). Addition of interaction “SES * depression” to Model 4

SES (ref. = high)

 Low SES

.618*

.254

0.12, 1.11

 Medium SES

.233

.195

-0.15, 0.62

Other Sociodemographic variables

 Sex (ref. = men)

.559***

.156

0.25, 0.87

 Age

-.005

.007

-0.02, 0.01

 Marital status (ref. = married)

  Unmarried

.110

.259

-0.40, 0.62

  Divorced

-.039

.279

-0.59, 0.51

  Widowed

-.433

.365

-1.15, 0.28

 Living without partner (ref. = living with partner)

-.058

.237

-0.52, 0.41

 Children < 18 years (ref. = no)

.079

.191

-0.30, 0.45

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

.135

.214

-0.28, 0.55

Headache-related variables

 Analgesic use (days a month)

.086***

.016

0.05, 0.12

 Headache duration (in years)

.002

.007

-0.01, 0.01

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

  4–14 days a month

1.212***

.210

0.80, 1.62

  > 14 days a month

.673

.448

-0.21, 1.55

 Migraine (ref. = no)

1.485***

.182

1.13, 1.84

Other health variables

 Physical inactivity (ref. = physical active persons)

.213

.158

-0.10, 0.52

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

.203

.184

-0.16, 0.56

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

.452

.752

-1.02, 1.93

Interaction

 SES * Depressive symptoms (ref. = high SES; no depressive symptoms)

  Low SES: depressive symptoms (ref. = no depressive symptoms)

-.077

.894

-1.83, 1.68

  Medium SES: depressive symptoms (ref. = no depressive symptoms)

.273

.793

-1.28, 1.83

 Model fitting: χ² (df)

272.77 (20) ***

 Goodness of fit

  (Pearson) χ² (df)

2183.62 (2248)

  (Deviance) χ² (df)

1652.73 (2248)

 Pseudo-R² (Nagelkerke`s)

.336

 Test of proportional odds: χ² (df)

58.85 (40)*