Background A critical appraisal of Global Burden of Disease (GBD) 2000 estimates for Major Depressive Disorder (MDD) identified an absence of reliable data and representative studies in many countries. GBD 2017 introduced methodological changes, amended inclusion criteria, and expanded the number of data sources. This study critically appraises the quality of the studies underpinning the GBD 2017 estimates for MDD with respect to i) the GBD 2017 inclusion criteria and ii) population coverage.

Methods Of 431 studies underpinning the GBD 2017 estimates, 400 were retrieved. Country-level samples used in multi-country studies were disaggregated to give 467 country-level studies. Each study was critically appraised with respect to the four GBD 2017 inclusion criteria: representativeness, study method and sample, diagnostic criteria and publication from 1980 onwards. Population coverage was calculated.

Results Less than half of studies (221/467, 47.32%) were nationally representative. Only 262/467 (56.10%) of studies reported specifically on MDD and more than a third did not use DSM or ICD criteria: 94/467 (20.13%) did not specify any diagnostic criteria and 68/467 (14.56%) relied on self-reported depression for diagnosis. Only 62/467 (13.28%) of studies were from 2011–2017. Only 107/195 (54.87%) of countries were covered by a single prevalence study.

Conclusion GBD 2017 estimates for MDD are based on incomplete country and population coverage. The inclusion of studies with non-representative populations, that do not use diagnostic criteria and the lack of specific data on MDD reduces the reliability of estimates and limits their value for policy making.