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Table 2 Feasibility criteria

From: Protocol for the STAR (Sheffield Treatments for ADHD) project: an internal pilot study assessing the feasibility of the Trials within Cohorts (TwiCs) design to test the effectiveness of interventions for children with ADHD

Criteria Measurement Criteria for continuation to a full trial
Recruitment to cohort rates Number recruited in 2 years % recruited/sample size estimation. Minimum acceptable to proceed to a full-scale trial will consider the number of years needed to recruit the required sample size. Numbers recruited in 2 years will be extrapolated to determine how long a full trial would need to be. The required sample size will be divided by the percentage recruited in 2 years. Duration of the full trial of more than 4 years will not be considered feasible.
Recruitment to treatment rates Percentage accepting offer At least 30%. The percentage of participants refusing treatment will be considered to determine acceptable levels of refusal. Too many treatment refusers may lead to a high chance of a type II error and inadequate information to estimate critical parameters for a full trial with reasonable precision.
Treatment effects (statistical significance) Standard mean difference (SMD) CGI Mean = < .3. Since neither intervention has been tested in this form previously, estimation of the effect size cannot consider previous estimates. Since we need to know that therapies show some evidence of being helpful, a SMD of 0.3 in those implementing the therapies will be considered sufficient to proceed to full trial.
Treatment effects (clinical significance) CGI T score 5 percentiles. A T score change of 5 percentiles is considered clinically significant, since the child has moved from one level of severity to another according to Conners (2009) [47].
Attrition: cohort Number of PQs returned at 6 months At least 30%
Attrition: consultations Number of consultations attended Adjustment of intervention provision
Acceptability of TQ and CQ Number of TQs and CQs completed at baseline and 6 months; number of email/telephone/ paper responses Adjustment of measure, collection methods and trial parameters. Questions reworded or removed dependent on discussion with carers and teachers, and optimum means of delivering questionnaires explored
Adverse events Clinicians records No severe adverse events as defined by the Common Terminology Criteria for Adverse Events guidelines
Appropriate outcome measurement Number of missing items Adjustment of measure
Recruitment of therapists Number recruited fulfilling criteria At least two for each therapy
Statistical analysis ANCOVA Meets assumptions