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In the absence of randomisation, observational studies must take extra care to create treatment groups that are comparable in terms of key characteristics. Various matching methods exist which can create sound comparisons, minimising confounding where possible. A recent observational study by Dal Negro et al. carried out a cost analysis comparing two asthma medications. They report strong conclusions which favour one treatment over the other, however they include little discussion on the limitations of their study. The purpose of this letter is to comment on the weaknesses of the study design, including the level of matching used, and to urge readers to consider these issues alongside the interpretation of results. [ABSTRACT FROM AUTHOR]

Aims: Continuous glucose monitoring (CGM) metrics can assist diabetes management. Consensus statements recommend > 70 % time in range (TIR) and ≤ 36 % glucose coefficient of variation (CV). However, how these targets perform in clinical practice is unknown. This retrospective, longitudinal cohort study analyzed relationships between TIR, CV, glycated hemoglobin (HbA1c), and hypoglycemia in a real-world setting., Methods: Data of 542 adults with type 1 diabetes who used CGM (January 2014-July 2020) were analyzed. Associations between TIR and HbA1c at the same and subsequent visits, incidence rate ratios (IRRs) for hypoglycemia at different CVs, and number of hypoglycemic events at cross-sections of HbA1c and CV were estimated by regression., Results: TIR was inversely related to HbA1c; for every 10 % increase in TIR, HbA1c was significantly reduced by 0.34 % (4 mmol/mol) and 0.20 % (2 mmol/mol) at the same and subsequent visits, respectively. Level 2 hypoglycemia was significantly reduced at CV < 30 %, 30-33 %, 33.1-36 %, and 36.1-40 %: adjusted IRRs vs CV ≥ 40.1 % of 0.14, 0.28, 0.32, and 0.50, respectively. Hypoglycemic events were reduced at lower CV across HbA1c levels and at higher HbA1c across CV levels., Conclusion: This study quantifies HbA1c improvements with increased TIR and hypoglycemia reductions with improved CV in clinical practice., Competing Interests: Declaration of competing interest M.P.-N., L.F., E.R.H., and Y.Y are employees of, and shareholders in, Eli Lilly and Company. R.J. was an Executive Director of Diabetes Global Medical Affairs at Eli Lilly and Company when he contributed to this article, and is currently a Senior Director, Clinical Development Strategy, at Novo Nordisk Inc., which provided no review of, or other support for, this article. R.B.M., S.L.E., and G.T.A. have no additional conflicts of interest to declare. V.N.S. has received honoraria from NovoNordisk, Medscape, Embecta, Insulet, Tandem Diabetes Care, Ascensia, and Dexcom for speaking, consulting or being on advisory boards, and his institution, University of Colorado, has received research support from NovoNordisk, Tandem Diabetes Care, Insulet, Alexion, Eli Lilly and Company, JDRF, and NIH (NIDDK & NIAMS)., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)