From principles to practice: the completeness of reporting and transparency of target trial emulations in Type 2 diabetes research

Despite the increasing application of target trial emulation (TTE) in type 2 diabetes mellitus (T2DM) research, the reporting completeness and transparency of TTE studies have not been comprehensively assessed. This study aimed to characterize item-level reporting of TTE studies in T2DM according to the Transparent Reporting of Observational Studies Emulating a Target Trial (TARGET) statement and to compare reporting before and after its publication. TTE studies in T2DM were searched on PubMed, Web of Science, and Embase. Two reviewers independently screened the records and extracted basic study characteristics, features of the target trial specification and its observational emulation, and item-level reporting completeness according to the TARGET statement. Reporting proportions were summarized descriptively and compared between studies published before and after the release of TARGET statement in 2025, with absolute differences and 95% confidence intervals. Of 1,580 records identified, 229 studies were included (93.0% published in 2024–2026). 157 were classified as pre-TARGET and 69 as post-TARGET; three studies could not be classified. Reporting was most complete for eligibility criteria, treatment strategies, outcomes, follow-up, and causal contrasts (96.9%–100.0% at the emulation stage), whereas the target trial assignment procedures (44.5%), the target trial data analysis plan (11.8%), identifying assumptions (5.7% for the specification; 2.6% for the emulation), and the frequency of missing data (3.5%) were infrequently reported. After the release of TARGET, reporting improved for causal contrasts (increasing 16.0% points; 95% CI, 4.7%–25.0%) and follow-up (increasing 11.0%; 95% CI, 0.5%–19.4%), whereas identifying assumptions (4.3% for the specification; 4.3% for the emulation) and the frequency of missing data (5.8%) remained underreported among post-TARGET studies. Although reporting of key TTE components was generally complete, important gaps remained in causal identifying assumptions and missing data. Greater adherence to the TARGET statement is needed to improve the transparency and completeness of TTE reporting. This systematic review finds that while causal estimands are generally well reported in both the target trial specification and its observational emulation in type 2 diabetes research, important gaps persist in reporting transparency and completeness. Key shortcomings include limited reporting of causal identifying assumptions and missing data. Future studies should enhance reporting completeness and transparency by stating causal identifying assumptions, reporting the frequency of missing data, and adhering more closely to the TARGET statement.