Design and Implementation of Observational Studies Emulating a Target Trial

Target trial emulation (TTE) is increasingly used to estimate causal effects with observational data, yet its clinical applications and methodologic quality remain unclear.

To characterize the clinical scenarios where TTE has been applied, assess methodologic limitations in design and implementation, and provide structured recommendations for strengthening future practice.

This cross-sectional study searched PubMed for TTE studies published from January 1, 2017, to December 15, 2023, in clinical journals in the top Journal Impact Factor quartile, supplemented by studies from 3 prior scoping reviews. Eligible studies explicitly aimed to emulate a target trial using observational data. Data were extracted using a standardized, consensus-based tool.

Study characteristics, application scenarios, specification of target trials, and adherence to 7 methodologic domains of TTE were evaluated. Recommendations were developed to address observed gaps.

Among 237 included studies, over half (128 [54.0%]) evaluated drug interventions, commonly in infectious diseases, cardiology, and oncology. TTE was applied in 8 recurring clinical scenarios, including randomized clinical trial replication and extending evidence to underrepresented populations or rare outcomes. TTE was most frequently applied to assess treatment effectiveness (165 studies [69.6%]), long-term outcomes (39 [16.5%]), emergency-use medications (42 [17.7%]), and active-treatment comparisons (49 [20.7%]). Major methodologic gaps were evident: only 134 studies (56.5%) developed a prespecified protocol, 127 (53.6%) did not review existing randomized clinical trials, and most that emulated existing trials (20 of 31 [64.5%]) or hypothetical trials (147 of 153 [96.1%]) did not justify the choice of trial to emulate. During implementation, 103 studies (43.5%) did not report all 7 methodologic components, 36 (15.2%) used postbaseline information inappropriately for eligibility, only 40 (16.9%) provided follow-up diagrams to define time zero, and only 73 (30.8%) addressed unmeasured confounding. A 5-step framework for target trial design and practical considerations for implementing methodologic principles was developed.

This cross-sectional study of TTE identified 8 common clinical scenarios for TTE application and substantial methodologic heterogeneity that threatened the credibility of resulting evidence. The study highlighted common pitfalls and proposed actionable recommendations to complement reporting standards such as the Transparent Reporting of Observational Studies Emulating a Target Trial guideline, which may support the generation of more robust observational evidence for clinical and policy decision-making.