Xuxi Zhang

As to the data of HbA 1c in each study, we extracted the mean and standard deviation (SD) of HbA 1c values of IG and CG at baseline and follow ‐ up intervals separately, and most eligible studies only reported HbA 1c values as “%”. Therefore, we used the NGSP’s HbA 1c converter at http://www.ngsp.org/convert1.asp to calculate HbA 1c values as both % and mmol/mol. If the study only provided the mean changes of HbA 1c at follow ‐ up intervals, then the mean values of IG and CG were calculated based on the mean changes and corresponding baseline mean of HbA 1c separately. 13, 21, 28, 31 What is more, if a study did not provide the SDs of mean values or data from which we can derive SDs at follow ‐ up intervals, then we used corresponding baseline SDs as the follow ‐ up interval SDs. 13, 21, 28, 31 If the study provided 95% Confidence Interval (CI) rather than SD of mean HbA 1c at baseline and follow ‐ up intervals, then the SD values were calculated based on corresponding 95% CI separately. 14; 18; 19 One study 16 provided standard error (SE) rather than SD of mean HbA 1c at baseline and follow ‐ up intervals. For this, we calculated the SD values based on corresponding SE values. We classified the complexity of intervention methods in two ways: 1) we classified the intervention methods into 3 categories based on the providers of peer support, including Peer ‐ leader ‐ intervention (PLI – peer support intervention led by one or several peer coaches, peer leaders, peer educators, peer supporters or peer mentors who were usually also patients but had received relevant training), Community ‐ health ‐ worker ‐ intervention (CHWI – intervention provided by nonprofessionals like community health workers, medical assistants, or community lay workers who had similar background or shared similar local culture with patients) and Peer ‐ partner ‐ intervention (PPI – intervention provided by patients themselves to help each other or to share experience together in a group, usually with no specific leader during the intervention); 2) we classified the intervention methods into 5 categories based on the approaches of peer support and setting, including Telephone ‐ dominant ‐ intervention (TDI – mainly providing peer support through regular telephone calls and sometimes combined with other methods like face ‐ to ‐ face contact), Support ‐ group ‐ intervention (SGI – mainly providing peer support through sharing experiences, setting goals and making plans and sometimes combined with relevant education at community setting), Home ‐ visit ‐ intervention (HVI – mainly providing peer support through home visits to educate the patients and help them to identify their difficulties and make plans to change their behaviors), Curriculum ‐ only ‐ intervention (CCOI – providing peer support through regular courses at community setting) and Curriculum ‐ combined ‐ reinforcement ‐ intervention (CCRI – providing peer support through regular courses in combination with other regular interventions like telephone calls, postcards, face ‐ to ‐ face contact, support group meetings and home visits to reinforce the effect of curriculums). We adopted the Cochrane Collaboration’s tool for assessing risk of bias which includes six domains: selection bias, performance bias, detection bias, attrition bias, reporting bias and other bias. 34 Two reviewers (Zhang and Yang) assessed each study independently and consulted Sun in the case of disagreements, all of which were then resolved by consensus. 132 Chapter 6