Qualitative evidence synthesis (QES) is a broad term, popularised within the Cochrane Collaboration, for the group of methods used to undertake systematic reviews of qualitative research evidence.
Guidelines
Authors should always consult current methods guidance at methods.cochrane.org/qi.
Flemming, K., Booth, A., Garside, R., Tunçalp, Ö., & Noyes, J. (2019). Qualitative evidence synthesis for complex interventions and guideline development: clarification of the purpose, designs and relevant methods. BMJ global health, 4(Suppl 1), e000882. Link
Other
Cochrane training: Chapter 21 Qualitative Evidence. Link
Cooke, A., Smith, D., & Booth, A. (2012). Beyond PICO: the SPIDER tool for qualitative evidence synthesis. Qualitative health research, 22(10), 1435–1443. Full Text
Odendaal, W. A., Anstey Watkins, J., Leon, N., Goudge, J., Griffiths, F., Tomlinson, M., & Daniels, K. (2020). Health workers' perceptions and experiences of using mHealth technologies to deliver primary healthcare services: a qualitative evidence synthesis. The Cochrane database of systematic reviews, 3(3), CD011942. Full Text