Howick J, et al. Effects of empathic and positive communication in healthcare consultations: a systematic review and meta-analysis. J R Soc Med 2018 111(7): 240–252. DOI: 10.1177/0141076818769477.
In the results of the abstract (but not the main text), it states that there were 28 eligible trials. There were 29 eligible trials, as stated in the body of the paper.