5The resulting scale is composed of (1) primary education, (2) lower secondary education, (3) upper secondary education, (4) post-secondary education, (5) first stage tertiary education (bachelor), (6) first stage tertiary education (master), and (7) second stage tertiary education.
Education was assessed in a seven-step categorization process ranging from none or pre-primary education (=0), to second stage tertiary education (=6), and introduced as a continuous variable.
Education has been measured with the international standard coding scheme (ISCED 1-digit) that distinguishes seven levels running from pre-primary or no education (0) to second stage tertiary education (6).
The different levels are primary education, lower secondary education, upper secondary education, tertiary education, and second stage of tertiary education.
As expected, students in the second stage of education are older and are more often living with a partner.
All mediating steps are separately analysed for students in the first and the second stage of education because we expect some cohort effects related to the stronger influence of the stage of life in the second stage.
The subjects were divided into two groups: (1) lower secondary, second stage of basic education, primary education, first stage of basic education or not completed primary education; (2) (upper) secondary, post secondary, first stage of tertiary or second stage of tertiary education.
Education was measured according to the International Standard Classification of Educational Degrees (ISCED-97) that we regrouped into 'low education' (pre-primary, primary or lower secondary education), 'medium education' (secondary or post-secondary education) and 'high education' (first and second stage of tertiary education).
Respondent's highest level of education was classified ranging from "not completed primary education" to "second stage of tertiary education" on a 7-point scale.
ISCED values range from 0 = pre-primary education to 6 = second stage of tertiary education.
For the sake of international comparison, we recoded the national educational categories into the worldwide International Standard Classification of Education classification 1997, as designed by UNESCO.10 The variable ranges from 1 (primary level of education and our reference value) to 6 (second stage of tertiary education, leading to an advanced research qualification).
