The Sleep sub-study was conducted within the Colombo Twin and Singleton Follow-up Study and determined the contribution of sleep and activity to the prevalence of metabolic syndrome and depression in Sri Lanka. It also aimed help to understand the potential for estimating the degree to which phenotypic correlations in sleep parameter are due to shared genetic or environmental factors as well. It is the first study conducted in a South Asian country to determine population based estimates of sleep parameters with a fixed 12 hour photo-period. Sleep duration and physical activity data were collected using actiwatches. Sleep diary and questionnaires helped to validate the collected data. The actiwatches were worn by participants for a period of 7 days. The collected data was analyzed and generated the journal article titled “Agreement between subjective and objective measures of sleep duration in a low-middle income country setting” .