Academic studies and grey literature were shortlisted in 2 stages: a review of the title and abstract or executive summary, followed by a review of the full text.
Lluniwyd rhestr fer o astudiaethau academaidd a llenyddiaeth lwyd mewn 2 gam: adolygiad o’r teitl a’r crynodeb neu grynodeb gweithredol, ac yn dilyn hynny adolygiad o’r testun llawn.