Table 1.

Definitions of primary and secondary sexual behaviour measures of this study

Primary sexual behaviour measures
Multiple partnerships	Having more than one sexual partner in the past 12 months.
Non‐regular partnerships	Having at least one sexual partner in the past 12 months who the participant was not married to or did not live with. This includes all non‐spousal, non‐cohabiting partners, including casual acquaintances and sex workers/clients.
Condomless non‐regular sex	Not using a condom during the last sexual intercourse with a non‐regular partner in the past 12 months among everyone who had a non‐regular partner in the past 12 months.
Population‐level condomless non‐regular sex	Not using a condom during the last sexual intercourse with a non‐regular partner in the past 12 months among everyone who had sex in the past 12 months. This measure covers the whole sexually active population, including those who did not have non‐regular partners.
Secondary sexual behaviour measures
Casual partnerships	Having at least one casual sexual partner in the past 12 months. This includes casual acquaintances and sex workers/clients. Casual partnerships represent a subset of non‐regular partnerships and are likely to be characterized by high HIV/STI infection risks.
Condomless casual sex	Not using a condom during the last sexual intercourse with a casual partner in the past 12 months among everyone who had a casual partner in the past 12 months.
Age at first sex	Age at which the participant first had sexual intercourse among those aged 20 to 29 years.

For further information on measures, including on survey questions and changes in measurement over time, see Supporting Information.