Ogilvie et al. BMC Public Health 2010, 10:703 http://www.biomedcentral.com/1471-2458/10/703 Enhanced activity monitoring studies In the year following their initial (’baseline’) survey, members of the study cohort are invited to opt in to additional in-depth studies. These provide for more detailed characterisation of differences both within and between the ‘intervention’ and ‘control’ groups after adjustment for baseline covariates. Household travel diaries All follow-up participants are invited to complete a seven-day household travel diary based closely on that used in the UK National Travel Survey [42] in addition to the core questionnaire survey. The index case (main participant) in each household is asked to complete the diary day by day during the seven day monitoring period with, or on behalf of, all mem- bers of their household. The purpose of the household travel diaries is: To enable exploration of the interrelationships of travel behaviour within households, such as the influ- ence of the need to take children to school en route to work, or the additional opportunity for car use by other members of the household created by a commuter’s decision to cycle to work and leave the car at home To provide more detailed travel data from which to estimate the effects of any changes in travel behaviour on overall household travel-related carbon emissions To provide a seven-day travel diary for the index case (main participant) in each household for compari- son with contemporaneous objective measurements where these are collected (see below). Enhanced objective measurement All members of the basic activity monitoring subgroup (those who complete Actigraph monitoring at baseline) are invited to opt in to enhanced objective measurement at follow-up. Instead of simply repeating seven days of Actigraph monitoring as at baseline, they are invited to undertake seven days of monitoring using both Actiheart com- bined heart rate and movement sensors and QStarz BT- Q1000X global positioning system (GPS) receivers. The accelerometer component of the Actiheart provides the equivalent of the follow-up Actigraph data for these par- ticipants [52]. Both Actiheart sensors and GPS receivers have been successfully used in previous free-living popu- lation studies [53,54]. The Actiheart is a lightweight waterproof device that clips onto two standard electro- cardiogram (ECG) electrodes on the chest and measures acceleration, heart rate, heart rate variability and ECG amplitude. It has been shown to be a valid and reliable tool for measuring both acceleration and heart rate and therefore offers a more accurate assessment of PAEE than accelerometry alone, particularly for activities such as cycling which are not optimally ascertained using hip-worn accelerometers [52]. Individual calibration is not required because a simple calibration protocol based on sleeping heart rate and gender has been shown to be Page 8 of 13 adequate for free-living studies [55]. Those who complete Actiheart data collection are offered more detailed individualised feedback on their activity data. The QStarz BT-Q1000X GPS receiver records the spa- tial coordinates (latitude and longitude) of participants at five-second intervals. Participants are asked to wear their GPS receivers during waking hours and recharge them each night - a simple procedure with which parti- cipants in previous studies have shown a high degree of compliance [54]. The purpose of enhanced objective measurement is to maximise the precision of measurement of travel beha- viour and estimation of PAEE in a subgroup of partici- pants, thereby providing robust objectively-measured data from which to: Determine the (combinations of) travel modes used by participants Estimate the PAEE involved in using different (com- binations of) modes of transport Test the hypothesis of activity substitution between domains (e.g. that an increase in active travel may be compensated for by a decrease in leisure-time physical activity) Estimate the contribution of active travel to overall PAEE and thereby estimate the effect of the intervention on overall PAEE Identify the physical characteristics of the routes used by participants to travel to and from work and thereby examine associations between route and other environmental characteristics and choice of travel mode. Longitudinal qualitative interview study Semi-structured interviews A purposive sample of par- ticipants (n~50) are invited to take part in a qualitative interview at baseline. These interviews are designed to explore the diverse practices and experiences of men and women, people in different age groups, people with and without access to a car, and people living in differ- ent areas. Interviews are conducted in participants’ homes, workplaces or other convenient locations at the participants’ choice and are semi-structured using a flex- ibly-applied topic guide. Each interview begins with an identification of the origin and destination of the partici- pant’s usual commuting journey, the usual route followed, the (combination of) mode(s) of transport usually used, and variations on the usual journey. The researcher then explores the reasons for these choices and variations (such as the need to transport children), the availability of alternatives, and what factors influence the choice between these options. Finally, the researcher explores whether participants have any expectation or intention of changing their travel mode choices, the bar- riers to and facilitators of making such changes, and their views as to why other people may have made other choices. Each interview is recorded using a digital voice