Box 1. Guidelines for the extraction of proportions
Response option	Method
Dichotomous (e.g. yes/no)	The proportion of participants choosing either ‘yes’ or ‘no’, depending on which indicated a negative attitude
Yes/unsure/no	The proportion of participants choosing either ‘yes’ or ‘no’, depending on which indicated a negative attitude
4‐point scale	The proportion of participants choosing ‘3’ or ‘4’ OR the proportion of participants choosing ‘1’ or ‘2’, depending on which indicated a negative attitude
5‐point scale	The proportion of participants choosing ‘4’ or ‘5’ OR the proportion of participants choosing ‘1’ or ‘2’, depending on which indicated a negative attitude
6‐point scale	The proportion of participants choosing within the range of 4–6 OR the proportion of participants choosing within the range of 1–3, depending on which indicated a negative attitude
7‐point scale	The proportion of participants choosing within the range of 5–7 OR the proportion of participants choosing 1–3, depending on which indicated a negative attitude
10‐point scale	The proportion of participants responding within the range of 1–4 OR the proportion of participants responding within the range of 7–10, depending on which indicated a negative attitude
100‐point scale	The proportion of participants responding within the range of 1–40 OR the proportion of participants responding within the range of 70–100, depending on which indicated a negative attitude