Table 1.

Key Characteristics of the methodology and design of the Seniors USP study, which contribute to objective activity data quality and compliance.

Key Characteristic	Component of methodology
Enabling 24-hour wear	monitor selection monitor and wear location combination was selected which allows the monitor to be worn 24 hours a day for at least one week (activPAL3 [PAL technologies, Glasgow, UK] on the front of the thigh)  waterproof monitor heat sealed (P200-C heat sealer [Packer, Essex, UK] ) within Layflat plastic tubing (75mm wide x 150m long x 250 gauge [Packer, Essex, UK]) to eliminate reasons why the monitor may be removed (e.g. bathing, swimming)  Opsite flexifix [Smith&Nephew, London, UK] waterproof dressing placed over the sealed monitor  reduce chances of skin irritation appropriate materials used: hypoallergenic adhesive pad (PALstickie [PAL technologies, Glasgow, UK]), medical grade waterproof dressing (Opsite flexifix); food-safe plastic tubing (Packer layflat tubing)  enhance comfort hypoallergenic adhesive pad (PALstickie) provided padding between the skin and the monitor/waterproof tube, and reduced the likelihood of skin irritation  edges of the waterproof pouch trimmed with some to spare, to avoid hard corners which might dig in the skin  schedule appointments to avoid removal scheduling appointments when the participant knew they were having medical treatment (e.g. involving hospitalisation), or were scheduled to fly (to avoid the need to remove for airport security) was actively avoided
Minimising Data Loss	test all monitors before starting data collection all monitors tested (we had 4 researchers wearing 13 monitors per leg) for multiple days before using them for data collection  monitors that were not functioning correctly identified and sought assistance from manufacturer  set minimum battery level for programming 4.1v (value obtained through experience) was used as a minimum battery level for programming the monitor, to avoid data loss through monitor stopping recording  use wide programming times programmed to start recoding immediately, to allow confirmation that the monitor was collecting data (flashing green light)  programmed to record for 14 days (minimum required for full data collection was 9 days) to allow for delays in starting to wear the monitor  trained staff applied the monitor ensured the monitors were applied appropriately  ensured waterproof dressing was applied properly, minimising potential for water ingress (and consequent data loss through removal or monitor stopping)  used a checklist on application, including re-checking monitor was recording data (flashing green light)  common misunderstandings/procedural shortcuts were pre-identified and addressed in training (e.g. highlighting tips and errors).  communication between participants and research staff a central contact point was provided for participants to discuss concerns with a study researcher, which reduced inappropriate monitor removal  communication between central experts and fieldworkers key diagnostic data logged by staff applying/removing the monitor, for example battery level at programming and downloading, whether green light flashing at application.  key diagnostic data recorded centrally (on a secure cloud server) allowing easy review by all staff  data recorded to increase compliance and allow identification of systematic errors/deviation from protocol and monitor malfunction  member of staff with experience of data collection using the monitor assigned to triage technical issues with using the monitor  early and continuous quality assurance checks allowed identification of individual and systematic deviations from protocol, immediate feedback to staff, and engagement in process  reducing opportunities to lose monitor monitor removed by researcher, which reduced reliance on participants for data retrieval, for example remembering to bring monitor to appointment, losing the monitor while not worn, accidentally washing monitor placed in pocket.
Quality Assurance	increasing confidence monitor was worn monitor removed by researcher, allowing confirmation monitor still worn after end of analysis period  a message was provided to participants that monitor should not require re-attachment during data collection. Additional material to allow reattachment was not provided. Participants were not asked to prospectively record if monitor was not worn  assurance that monitor had not been reattached by participant was provided by using attachment materials that are not commonly available to participants  In the case that the monitor was removed by participant prior to research appointment, we then asked retrospectively for date and time of removal. This was close to date of removal to allow for reasonable recall, and was then checked with data record. Data processing was from midnight-midnight and not from specific time of removal, so day/date of removal was sufficient information  data inspection routinely performed by a single researcher close to time collected; difficult cases resolved by discussion with a second researcher  hierarchical review process was used (weekly graphical display, daily graphical display, raw acceleration data), to speed up routine cases but maintain in-depth review when required.  conducted with confidence that monitor was on the leg during data collection (i.e. looking for issues in battery/monitor failure, or thresholds not appropriate, e.g. known not to collect shuffling gait at slow speeds)