• Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA. charles.matthews2@nih.gov.
• Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, MD, USA.
• Department of Epidemiology and Preventive Medicine, University of Regensburg, Regensburg, DE, Germany.
• School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, AU, Australia.
• Department of Health Kinesiology and Recreation, University of Utah, Salt Lake City, UT, USA.
• Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD, USA.
• School of Health Sciences, University of South Australia, Adelaide, AU, Australia.
• Department of Kinesiology, Iowa State University, Ames, IA, USA.

BACKGROUND: The last few years have seen renewed interest in use-of-time recalls in epidemiological studies, driven by a focus on the 24-h day [including sleep, sitting, and light physical activity (LPA)] rather than just moderate-vigorous physical activity (MVPA). This paper describes four different computerised use-of-time instruments (ACT24, PAR, MARCA and cpar24) and presents population time-use data from a collective sample of 8286 adults from different population studies conducted in Australia/New Zealand, Germany and the United States.

METHODS: The instruments were developed independently but showed a number of similarities: they were self-administered through the web or used computer-assisted telephone interviews; all captured energy expenditure using variants of the Ainsworth Compendium; each had been validated against criterion measures; and they used a domain structure whereby activities were aggregated under categories such as Personal Care and Work.

RESULTS: Estimates of physical activity level (average daily rate of energy expenditure in METs) ranged from 1.53 to 1.78 in the four studies, strikingly similar to population estimates derived from doubly labelled water. There was broad agreement in the amount of time spent in sleep (7.2-8.6 h), MVPA (1.6-3.1 h), personal care (1.6-2.4 h), and transportation (1.1-1.8 h). There were consistent sex differences, with women spending 28-81% more time on chores, 8-40% more time in LPA, and 3-39% less time in MVPA than men.

CONCLUSIONS: Although there were many similarities between instruments, differences in operationalizing definitions of sedentary behaviour and LPA resulted in substantive differences in the amounts of time reported in sedentary and physically active behaviours. Future research should focus on deriving a core set of basic activities and associated energy expenditure estimates, an agreed classificatory hierarchy for the major behavioural and activity domains, and systems to capture relevant social and environmental contexts.