Average systolic blood pressure is the pressure in the arteries when the heart beats (contracts). This variable is measured with a mercury sphygmomanometer by trained research assistants using the Hypertension Detection and Follow-up Program protocol. For each participant, blood pressure readings are taken as follows:

1. Seated blood pressure reading (trial 1)
2. Seated blood pressure reading (trial 2)
3. Standing blood pressure reading, 1 minute later

Average systolic blood pressure is calculated by averaging the three systolic blood pressure readings and is expressed in mmHg.