In the version of this Comment originally published, the Acknowledgements section was missing information about the support from the National Institutes of Health Science of Behavior Change Common Fund Program; the full text should have read 'This work was supported by the National Institutes of Health (NIH) Science of Behavior Change Common Fund Program through an award administered by the National Institute on Aging (U24AG052175) and by a Wellcome Trust collaborative award (The Human Behaviour-Change Project: Building the science of behaviour change for complex intervention development, 201,524/Z/16/Z).' This has now been corrected in all versions.