Table 2 Stop–go feasibility criteria

Acceptability of methodology

Recruitment & retention rates as below

End of recruitment (week 8)

Compliance

Mean attendance < 10 sessions

Mean attendance < 14 sessions

Mean attendance 14 sessions

Mean attendance 14 + sessions

End of int. (week 22)

End interviews

Unfavourable views, serious concerns

Unfavourable views, suggestions for modification

Favourable views, suggestions for modification

Favourable views, no concerns

1 month post-intervention (week 26)

Feasibility of recruitment processes

Screening rates

Identify < 50 potentially eligible subjects

Identify < 100 potentially eligible subjects

Identify 100–128 potentially eligible subjects

Identify > 128 potentially eligible subjects

End of recruitment

Recruitment rates

Recruit < 50% of sample size

N < 25 in 8 weeks, < 5% per week

N = 25–30 in 8 weeks, < 13% per week

N = 30 in 8 weeks, 13% per week or greater

End of recruitment

Participation rates

Participation rate < 5%

Participation rate 5–15%

Participation rate 15–25%

Participation rate 25% or greater

6 months post-intervention

Retention rates

Attrition > 75%

Attrition 50–75%

Attrition 30–50%

Attrition < 30%

6 months post-intervention

End interviews

N/A

Major suggestions to improve recruitment processes

Minor suggestions to improve recruitment processes

No suggestions to improve expressed

1 month post-intervention (week 26)

Identify N eligible participants, participant rates and retention rates

N identified by HCPs

 < 50 identified

50–100 identified

100–128 identified

 > 128 potentially eligible identified

End of recruitment

N expressing interest

 < 30 express interest

30–40 express interest

40–60 express interest

 > 60 express interest

End of recruitment

N providing consent

 < 15 provide consent

15–25 provide consent

25–30 provide consent

30 provide consent

End of recruitment

N lost to follow-up

Attrition > 75%

Attrition 50–75%

Attrition 30–50%

Attrition < 30%

1 month post-intervention, 3 and 6 months post-intervention

Researcher time and costs per participant

Researcher diary

N/A

Researcher time exceeds allocated time requiring additional study support

Researcher time and cost only just covers time required

Researcher time and cost fully covers time required

6 months post-intervention

Appropriate outcome measures

Variability of outcome

Estimate of control mean and SD of change

No difference or clinically important difference favouring control detected based on confidence limits

Difference cannot be detected based on confidence limits but data suggests improvement favouring intervention

Difference can be detected based on confidence limits

Clinically important difference can be detected based on confidence limits

End of intervention

Intervention components

Therapist adherence

Adherence < 50%

Adherence < 50%

Adherence 50–75%

Adherence > 75%

End of intervention

End interviews

Serious concerns expressed regarding intervention

Major suggestions to adapt intervention

Minor suggestions to adapt intervention

No concerns or suggestions to adapt intervention

Intervention adherence

Therapist self-rated adherence

Video rated adherence

Adherence < 25%

Adherence 25–50%

Adherence 50–75%

Adherence > 75%

End of intervention

Estimate of cost of intervention and services received

Therapist time

CSRI

Cost significantly greater than usual care, no potential to modify intervention, no indication of benefits

Cost is greater than usual care—intervention may be modified, but outcomes suggest some benefits

Cost is greater than usual care but outcomes strongly suggest benefits

Cost is equivalent to or slightly greater than usual care, outcomes strongly suggest benefits

6 months post-intervention