Table 1.

Construction of Bridging score.

Bridge score component	Question in survey	Score
		0	1
Ethnicity	What proportion of your friends are of the same ethnic group as you?	“All similar”	“More than half”, “about half”, or ‘less than half”
Age	What proportion of your friends are of a similar age as you?	“All similar”	“More than half”, “about half”, or ‘less than half”
Income	What proportion of your friends have a similar level of education as you?	“All similar”	“More than half”, “about half”, or ‘less than half”
Education	What proportion of your friends have similar incomes to you?	“All similar”	“More than half”, “about half”, ‘less than half”

Notes: Our Bridging score takes values between 0 and 4, is calculated from the sum of 4 scores from individual Bridge score components (0 being worst, 4 being best).