Managers might also consider asking about potentially important issues, such as traffic accidents while reading messages on a mobile phone. Data could be collected by continuous reporting, monitoring (e.g. surveys) and scheduled evaluations involving either all participants, subsamples or whole populations. A useful process indicator is the opt-out rate. The sample size for an evaluation of effectiveness should be based on pre-identified diversity in the population (e.g. geography, income, diabetic versus non-diabetic).