Randomised controlled trials are the most effective way to differentiate between the effects of competing interventions. However, head-to-head studies are unlikely to have been conducted for all competing interventions.
ASJC Scopus subject areas
Edwards, S. J., Clarke, M., Wordsworth, S., & Borrill, J. (2009). Indirect comparisons of treatments based on systematic reviews of randomised controlled trials. International Journal of Clinical Practice, 63(6), 841-854. https://doi.org/10.1111/j.1742-1241.2009.02072.x