Socio-demographic variables
The demographic variables were self-reported age and gender. Additional socio-demographic variables included education and income levels. Education was categorised into the following levels based on the German school system: ‘no school graduation’, ‘10 years of education’,
‘12 years of education’, ‘13 years of education’ and ‘first university degree or higher’. Household net income per month was assessed in nine categories and summarised in three groups based on tertiles: ‘low income’ (< 1500€), ‘mid- dle income’ (1500€–2499€), and ‘high income’ (€ > 2500€).