App screening process

The sample was identified from 400 highly ranked free and paid apps from the ‘Health & Fitness category’ in iTunes and Google Play stores to represent the apps that were most visible to the user. This method of assessing popularity has been used in other studies assessing apps.^27–29

The inclusion criteria were:

Behaviour targeted is PA.

The app targets adults.

The app had stand-alone functionality (i.e. does not need to be linked with peripheral devices, such as pedometers; and does not require paid membership to access the app).

Exclusion criteria:

Primary aim of the app is focused on multiple behaviours or behavioural outcomes (e.g. apps targeting both PA and diet), as it would be difficult to compare apps targeting multiple health behaviours.

The app focuses on increasing PA as part of management of a long-term condition, as it may not be comparable to apps targeting PA levels in healthy individuals.

Apps sold in a pack (i.e. ‘bundle’) were excluded, as it is impossible to extract the popularity ranking from a pack of multiple apps. These apps are very often positioned within the ranks separately.