DNA methyltransferase inhibitors (DNMTIs) for patients with higher risk myelodysplastic syndromes (HR-MDS) have low complete remission rates and are not curative. Early DNMTI combination clinical trials in HR-MDS are often termed "promising", but many randomized trials subsequently failed to show benefit. Clearer understanding when a combination is likely to improve upon DNMTI monotherapy would inform randomized studies. We reviewed MDS azacitidine or decitabine monotherapy studies. We collected baseline demographics including IPSS risk, DNMTI, disease characteristics; and response variables including survival, marrow and hematologic responses. Aggregate estimates across studies were calculated using meta-analyses techniques. Using a binomial design, we estimated the necessary operating characteristics to design a phase II study showing improved efficacy of a combination over monotherapy. Among 1908 patients the overall response rate ORR was 24% (n=464, 95%CI 0.22-0.26): 267 complete response (CR, 14%), 68 partial response (PR, 4%) and 129 marrow complete remission (mCR, 7%). Among 1604 patients for whom a hematologic response was reported, 476 patients (30%, 95%CI 0.27-0.32) reported hematologic improvement (HI). More patients treated with azacitidine achieved HI (38%, 95%CI 0.35-0.41) compared to decitabine (15%, 95%CI 0.13-0.19), while the marrow ORR rate was higher with decitabine (29%,95%CI 0.26-0.33) compared to azacitidine (21%, 95%CI 0.19-0.23). CR rates were similar between DNMTIs: 13% with azacitidine and 16% with decitabine. Variables that influence MDS response include the specific DNMTI backbone and the distribution of IPSS risk of patients enrolled on a trial. Considering these factors can help identify which early combination approaches are worth assessing in larger randomized trials.