Bariatric surgery and all‐cause mortality: A methodological review of studies using a non‐surgical comparator
Authors' conclusion
Several important sources of bias were identified in non-randomized studies of the effectiveness of bariatric surgery versus non-surgical comparators on mortality. Future studies should ensure that confounding by BMI is accounted for, considering the choice of the comparator group, and that the design or analysis avoids immortal time bias from the misclassification or exclusion.
Study context
- Population
- Non-randomized studies (PubMed) of bariatric surgery vs non-surgical patients on all-cause mortality21 cohort studies
- Comparison
- Bariatric surgery vs non-surgical patients
- Outcome
- Sources of bias
Methodological detailsbias analyses
- Bias analyses
Main finding
As reported in the abstract
Studies affected by immortal time bias (misclassification or exclusion of follow-up time)
11
Studies with potential confounding bias from lack of body mass index (BMI) adjustment
5
BMI confounding bias analysis shifted estimates towards the null: reported HR vs bias-adjusted HR
0.78 vs. 0.92
Immortal time bias analysis (2-year wait time) shifted estimates towards the null: reported HR vs bias-adjusted HR
0.57 vs. 0.81
Original publication
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