Phase I can be undertaken by a FTE post-doctoral qualitative researcher in about three to four months. Phase II requires around six to nine months for implementation and impact. This can vary considerably, depending on the complexity of the RCT and the issues that need to be addressed. The usual cost is around £60-70k for a 12 month QRI (as detailed below). Costs for a QRI lasting 12 months: time for RA (post-doc) FTE £25k; time for Donovan or senior member of team ( or FTE) £7-10k; University of Bristol indirect/estates c. £28k; consumables (travel, recorders, transcription) c. £5k.
The number of treatment units (subjects or groups of subjects) assigned to control and treatment groups, affects an RCT's reliability. If the effect of the treatment is small, the number of treatment units in either group may be insufficient for rejecting the null hypothesis in the respective statistical test . The failure to reject the null hypothesis would imply that the treatment shows no statistically significant effect on the treated in a given test . But as the sample size increases, the same RCT may be able to demonstrate a significant effect of the treatment, even if this effect is small. 
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