David A McAllister

Aim: This simulation study is to assess the utility of physician's prescribing preference (PPP) as an instrumental variable for moderate and smaller sample sizes. Materials & methods: We designed a simulation study to imitate a comparative effectiveness research under different sample sizes. We compare the performance of instrumental variable (IV) and non-IV approaches using two-stage least squares (2SLS) and ordinary least squares (OLS) methods, respectively. Further, we test the performance of different forms of proxies for PPP as an IV. Results: The percent bias of 2SLS is around approximately 20%, while the percent bias of OLS is close to 60%. The sample size is not associated with the level of bias for the PPP IV approach. Conclusion: Irrespective of sample size, the PPP IV approach leads to less biased estimates of treatment effectiveness than OLS adjusting for known confounding only. Particularly for smaller sample sizes, we recommend constructing PPP from long prescribing histories to improve statistical power.

Background This network meta-analysis aimed to compare the effects of bariatric surgery, novel glucose-lowering agents (SGLT2i, GLP1RA, DPP4i), and insulin for patients with type 2 diabetes mellitus (T2DM) and obesity. Methods Four databases were searched from inception to April 2023 to identify randomized controlled trials (RCTs) comparing bariatric surgery, SGLT2i, GLP1RA, DPP4i, insulin, and/or placebo/usual care among patients with T2DM and obesity in the achievement of HbA1c < 7.0 per cent within one year, and 12-month changes in HbA1c and body weight. Results A total of 376 eligible RCTs (149 824 patients) were analysed. Bariatric surgery had significantly higher rates of achieving HbA1c < 7.0 per cent than SGLT2i (RR = 2.46, 95 per cent c.i. = 1.28, 4.92), DPP4i (RR = 2.59, 95 per cent c.i. = 1.36, 5.13), insulin (RR = 2.27, 95 per cent c.i. = 1.18, 4.58) and placebo/usual care (RR = 4.02, 95 per cent c.i. = 2.13, 7.93), but had no statistically significant difference from GLP1RA (RR = 1.73, 95 per cent c.i. = 0.91, 3.44), regardless of oral (RR = 1.33, 95 per cent c.i. = 0.66, 2.79) or injectable (RR = 1.75, 95 per cent c.i. = 0.92, 3.45) administration. Significantly more GLP1RA patients achieved HbA1c < 7.0 per cent than other non-surgical treatments. Bariatric surgery had the greatest reductions in HbA1c (∼1 per cent more) and body weight (∼15 kg more) at 12 months. Among novel glucose-lowering medications, GLP1RA was associated with greater reductions in HbA1c than SGLT2i (−0.39 per cent, 95 per cent c.i. = −0.55, −0.22) and DPP4i (−0.51 per cent, 95 per cent c.i. = −0.64, −0.39) at 12 months, while GLP1RA (−1.74 kg, 95 per cent c.i. = −2.48, −1.01) and SGLT2i (−2.23 kg, 95 per cent c.i. = −3.07, −1.39) showed greater reductions in body weight than DPP4i at 12 months. Conclusion Bariatric surgery showed superiority in glycaemic control and weight management compared to non-surgical approaches. GLP1RA administered by oral or injectable form demonstrated reduced HbA1c and body weight at 12 months, and was preferable over other non-surgical treatments among patients with T2DM and obesity. PROSPERO registration no CRD42020201507