Trial Forge Guidance 2: how to decide if a further Study Within A Trial (SWAT) is needed

Table 2 The cumulative effect estimates for the two telephone reminders compared to no reminder studies included in the updated Cochrane recruitment interventions review [1]

	Total number of participants	Intervention (n recruited/N invited)	Control (n recruited/N invited)	Baseline (control) recruitment rate	Effect estimate (95% CI)
Nystuen, 2004 [25] (Telephoning people aged 16–66 years who had not responded to initial invitation by 2 weeks. Comparator was no call. Calls were made by research team. People were being recruited to a return to work trial for people on sick leave for > 7 weeks).	498	31/256	11/242	4.5%	8% (3%–12%)
Wong, 2013 [26] (Telephoning people aged 50–70 years who had not responded to initial invitation by 4 weeks. Comparator was no call. Calls were made by research nurses. People were being recruited to a colorectal cancer screening trial).	952	59/480	35/472	7.4%	5% (1%–9%)
Cumulative results (Nystuen + Wong)	1450	90/736	46/714	6.0% (mean)	6% (3%–9%)

The GRADE rating of the certainty in the evidence is high
1. Both trials are scored as low risk of bias on the Cochrane Risk of bias tool
2. The results are consistent
3. The outcome was direct
4. The results are not imprecise; the confidence intervals are not too large and wholly on the side of benefit
5. There are too few trials for an assessment of publication bias and we have assumed that there is none
NOTE: the evidence for this intervention comes entirely from trials with low (< 10%) underlying recruitment. When applied to trials with higher recruitment we would downgrade the GRADE assessment because of Indirectness to moderate

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