Using Negative Control Outcomes and Difference-in-Differences Analysis to Estimate Treatment Effects in an Entirely Treated Cohort: The Effect of Ivacaftor in Cystic Fibrosis
Autor: | Siobhán B. Carr, Simon Newsome, Ruth H. Keogh, Rhian Daniel, Diana Bilton |
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Rok vydání: | 2021 |
Předmět: |
longitudinal data
medicine.medical_specialty Cystic Fibrosis Epidemiology Population Cystic Fibrosis Transmembrane Conductance Regulator Negative control Quinolones Aminophenols Cystic fibrosis Ivacaftor Internal medicine medicine Humans negative control outcomes Benzodioxoles causal inference education G551D 01 Mathematical Sciences 11 Medical and Health Sciences Public Environmental & Occupational Health education.field_of_study Science & Technology difference-in-differences analysis business.industry medicine.disease Difference in differences Confidence interval cystic fibrosis transmembrane conductance regulator (CFTR) modulators Intravenous antibiotics Mutation Cohort ivacaftor business Life Sciences & Biomedicine medicine.drug |
Zdroj: | American Journal of Epidemiology. 191:505-515 |
ISSN: | 1476-6256 0002-9262 |
DOI: | 10.1093/aje/kwab263 |
Popis: | When an entire cohort of patients receives a treatment, it is difficult to estimate the treatment effect in the treated because there are no directly comparable untreated patients. Attempts can be made to find a suitable control group (e.g., historical controls), but underlying differences between the treated and untreated can result in bias. Here we show how negative control outcomes combined with difference-in-differences analysis can be used to assess bias in treatment effect estimates and obtain unbiased estimates under certain assumptions. Causal diagrams and potential outcomes are used to explain the methods and assumptions. We apply the methods to UK Cystic Fibrosis Registry data to investigate the effect of ivacaftor, introduced in 2012 for a subset of the cystic fibrosis population with a particular genotype, on lung function and annual rate (days/year) of receiving intravenous (IV) antibiotics (i.e., IV days). We consider 2 negative control outcomes: outcomes measured in the pre-ivacaftor period and outcomes among persons ineligible for ivacaftor because of their genotype. Ivacaftor was found to improve lung function in year 1 (an approximately 6.5–percentage-point increase in ppFEV1), was associated with reduced lung function decline (an approximately 0.5–percentage-point decrease in annual ppFEV1 decline, though confidence intervals included 0), and reduced the annual rate of IV days (approximately 60% over 3 years). |
Databáze: | OpenAIRE |
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