Table 4.

Barriers to participation and drop-out or refusal rates of participants

Reasons for refusal to participate or drop-out	Proportion of participants who refuse participation	References
Appointment non-attendance	14.0% of passive refusals	[40]
	2.1% of males that refused to participate	[58]
	1.3% of males were unable to cope with study requirements due to old age	[58]
Comprehension of the study requirements	0.4% of males refused to participate	[58]
Cannot be bothered/not interested	27.8% of active refusals	[40]
	13.8% declined to participate	[41]
	66.7% refused to participate	[44]
	39.6% males that refused to participate	[58]
	18.5% of eligible participants	[49]
Did not meet inclusion criteria	87% of eligible participants	[49]
Time commitment	38.9% of active refusals	[40]
	26.3% of males that refused to participate	[58]
Invasion of privacy	0.3% of males that refused to participate	[58]
Medical	15.5% of participants who refused to participate	[57]
	35.6% of participants unable to attend due to illness, 0.2% of participants had limited medical information	[40]
	16.9% of males that refused to participate	[58]
Unable to contact/no response	35.0% of eligible participants	[40]
	17.4% of eligible participants	[41]
	40.7% of invited male participants	[61]
Psychopathology factors	0.8% of males refused to participant in case a medical problem was uncovered	[58]
Reluctance over medical testing	1.1% of males that refused to participate	[58]
Religious/philosophical reasons	0.1% of males that refused to participate	[58]
Third party involvement	62.2% of participants passively refused via a relative, 15.9% of participants passively refused by resident/nursing home	[40]
	18.4% transferred to another ward or discharged from hospital or research nurse forgot to ask	[44]
Unknown reason/personal reason	5.2% of males that refused to participate	[58]
	9.5% of eligible participants in 1968	[45]
	28.6% of active refusals	[40]
	3.2% of eligible participants	[41]
	3.6% of eligible participants	[49]
	Proportion of participants who were non-completers/Further suggestions for improvements by completing participants
Appointment non-attendance	3.2% of non-completers	[41]
	24.7% missed at least one visit by end of study (12 months)	[52]
	Quantitative data- in person visits were difficult to attend due to the distance of the centre	[53]
Communication	Qualitative data- better coordination of communication for study results to participants	[38, 49]
	Qualitative data- increased personalisation would increase engagement like a personal question the participants could contemplate over the next week	[49]
	Qualitative data- increase of data sharing between research team, treatment therapist and each participant would have increased engagement and data tracking over the period	[49]
Education	Qualitative data- Increasing the education around the condition that is the focus of the trial	[38]
Medical	12.7% non-completers	[57]
	4.1% of non-completers had a child that had an additional diagnosis	[51]
	Qualitative data- state of the participants personal health and the nature of the intervention may affect future enrolment	[38]
Situational (lack of reliable housing, moving, death)	1.4% of non-completers	[57]
	95.2% of non-completers	[42]
	1.4% of non-completers from wave 1 (1974) to 47.3% in wave 5 (2011)	[45]
	6.8% to 30.6% of non-completers across 6 different centres	[61]
	25.7% of non-completers moved, 5.4% of families had a child who died	[51]
	21.4% of non-completers died, 17.4% moved away	[36]
	2.3%—9.4% of non-completers (wave 1–5)	[39]
	Qualitative data- unable to complete exercise or have appropriate meal preparation	[53]
	63.4% of non-completers	[55]
	35.5% of non-completers died	[48]
Inability to adhere to study activities	Qualitative data- unable to complete training due to unreliable technology	[53]
	12.7% of non-completers	[57]
	10.1% did not receive allocation of intervention	[41]
	1.7% of non-completers did not like research assessment, 0.8% of non-completers were incarcerated	[48]
Cannot be bothered/ loss of interest/wanted to withdraw	40.8% of non-completers	[36]
	9.5% of non-completers	[51]
	3.2% of non-completers	[44]
	20.6% of non-completers	[61]
	13.2% of non-completers	[48]
Difficulty to arrange follow-up appointments with participants	6.8% of non-completers	[51]
	20.6% of non-completers	[48]
Missing data/incomplete data	6.5% of participants	[41]
	52.5% of participants did not complete the final postal survey, 0.36% of participants did not have available data in the Finnish national Care Register for Health Care	[44]
	15.0% of non-completers	[61]
	3.1% of participants	[43]
Time commitment	5.6% of non-completers	[57]
	17.6% of non-completers	[51]
	Qualitative data- competing demands in personal life, unable to prioritize program participation	[53]
	Qualitative data- 24-h urine output collection during work hours was difficult and restrictive, taking days of work and losing wages	[38]
Lost contact	8.5% of non-completers	[57]
	27.8% of non-completers	[44]
	1.7% of non-completers	[48]
Unknown reason/personal reason	7.0% of non-completers	[57]
	4.8% of non-completers	[42]
	4.8% of non-completers	[44]
	21.6% of non-completers	[51]
	20.9% of non-completers from wave 1 (1974) to 24.1% in wave 5 (2011)	[45]
	10.7% of non-completers	[56]
	57.5% of non-completers were lost by 1-year follow up	[46]
	16.5% of non-completers	[48]
Difficulty in comprehending the study	2.7% of non-completers	[51]
	Qualitative data- reducing length and complexity of questionnaires and understanding the potential risks	[38]
Psychopathology factors	Paranoid factor had an elevated but non-significant risk for early drop out (26.9%) Dysphoric Borderline factor put a significant risk for late dropout (15.9%)	[50]
	Qualitative data- side effects from medications for mental health or chronic pain were issues in completing the program. Social anxiety of talking openly to other participants also prohibited some participants interaction	[53]
Third party involvement	6.8% of non-completers – due to family issues	[51]
	Qualitative data- consider withdrawing when family was sick	[38]
	4.2% of non-completers—Work and family responsibilities	[48]
Financial Hardship	Qualitative data- participants across all treatment groups found recommendations of what to eat and how to exercise cost prohibitive	[53]
	Qualitative data- providing monetary incentives	[38]
Technical Issues	Qualitative data- difficulties in troubleshooting web-based program after logging in as well as printing physical activity log	[53]