Table 1.

Number and percentage of studies satisfying each quality criterion (See supplementary material 2 for assessment of each paper)

Criteria	Number of papers (n = 22)	Percentage
Explicit theoretical framework and/or literature review	21	95%
Aims and objectives clearly stated	21	95%
Clear description of context	21	95%
Clear description of the sample and how it was recruited	17	77%
A clear description of methods used to collect and analyse data	14	64%
Attempts made to establish the reliability or validity of data analysis	8	36%
Inclusion of sufficient original data to mediate between evidence and interpretation	16	73%