Causal analyses with target trial emulation for real-world evidence removed large self-inflicted biases: systematic bias assessment of ovarian cancer treatment effectiveness

•To assess potential biases in real-world evidence (RWE), this paper compares the hazards ratio (HRs) of the reference trial to the estimated HRs following different analytic approaches.•Biases resulting from the different analytic approaches varied in size and direction, ranging from 75% underestimating the HR to 36% overestimating the HR.•The full causal analysis (including the target trial emulation using a marginal-structural-Cox-model) yielded the smallest bias, overestimating the HR by 10%.•In RWE, a thorough causal-inference-based design and analysis is important.