Robert W Platt

Robert W Platt
McGill University | McGill · Department of Epidemiology, Biostatistics and Occupational Health

PhD

About

528
Publications
51,882
Reads
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27,496
Citations
Additional affiliations
January 2011 - present
Jewish General Hospital
Position
  • Senior Investigator
October 1996 - present
McGill University
Position
  • Professor (Full)
October 1996 - present
McGill University Health Centre
Position
  • Investigator

Publications

Publications (528)
Article
In biomedical studies, survival data with a cure fraction (the proportion of subjects cured of disease) are commonly encountered. The mixture cure and bounded cumulative hazard models are two main types of cure fraction models when analyzing survival data with long-term survivors. In this article, in the framework of the Cox proportional hazards mi...
Article
Full-text available
Gestational diabetes mellitus (GDM) increases the risk of early-onset type 2 diabetes, which further exacerbates the risk of developing diabetic complications such as kidney, circulatory, and neurological complications. Yet, existing models have solely focused on the prediction of type 2 diabetes, and not of its complications, which are arguably th...
Preprint
Full-text available
Predictor identification is important in medical research as it can help clinicians to have a better understanding of disease epidemiology and identify patients at higher risk of an outcome. Variable selection is often used to reduce the dimensionality of a prediction model. When conducting variable selection, it is often beneficial to take selecti...
Poster
Full-text available
Evidence suggests that beta-blockers increase the risk of hypoglycemia. However, their effects among users of sulfonylureas, drugs that also cause hypoglycemia, are not well understood. Thus, our study assessed the potential association between concomitant use of sulfonylureas and beta-blockers and the risk of severe hypoglycemia. This retrospectiv...
Article
Aims: To compare the risk of cardiovascular outcomes with long-acting insulin analogues versus Neutral Protamine Hagedorn (NPH) insulin among patients with type 2 diabetes. Materials and methods: We conducted a population-based retrospective cohort study, using the United Kingdom Clinical Practice Research Datalink Aurum, linked with hospitaliza...
Article
Background: Time-related biases, such as immortal time and time-window bias, frequently occur in pharmacoepidemiologic research. However, the prevalence of these biases in perinatal pharmacoepidemiology is not well understood. Objective: To describe the frequency of time-related biases in observational studies of medications commonly used during...
Article
Full-text available
Background With many disease-modifying therapies currently approved for the management of multiple sclerosis, there is a growing need to evaluate the comparative effectiveness and safety of those therapies from real-world data sources. Propensity score methods have recently gained popularity in multiple sclerosis research to generate real-world evi...
Preprint
Objective To update a recently published analysis exploring the causal association between positron emission tomography (PET)-measured change in brain β-amyloid plaque and cognitive decline in patients with Alzheimer’s disease (AD) enrolled in randomized clinical trials (RCTs). Design Updated instrumental variable meta-analysis. Setting Sixteen R...
Article
Aims: Studies using contemporary cohorts are needed to assess the association between type 2 diabetes and cancer. Methods: Using the United Kingdom Clinical Practice Research Datalink, we matched patients with type 2 diabetes between 1988 to 2019 to patients without type 2 diabetes. Poisson regression models were fit to estimate incidence rate r...
Article
Full-text available
Many studies seek to evaluate the effects of potentially harmful pregnancy exposures during specific gestational periods. We consider an observational pregnancy cohort where pregnant individuals can initiate medication usage or become exposed to a drug at various times during their pregnancy. An important statistical challenge involves how to defin...
Preprint
Full-text available
In the statistical literature, a number of methods have been proposed to ensure valid inference about marginal effects of variables on a longitudinal outcome in settings with irregular monitoring times. However, the potential biases due to covariate-driven monitoring times and confounding have rarely been considered simultaneously, and never in a s...
Article
Background: Although gestational diabetes might be more common in twin versus singleton pregnancies, reasons for this are unclear. We evaluated the extent to which the relationship is explained by higher mid-pregnancy weight gain within normal weight and overweight pre-pregnancy body mass index (BMI) strata. Methods: We analyzed serial weights a...
Conference Paper
Introduction: Although long-acting insulin analogs (glargine, detemir, and degludec) and neutral protamine Hagedorn (NPH) insulin show similar efficacy for glycemic control among patients with type 2 diabetes, their comparative effectiveness in reducing cardiovascular events is unclear. Objective: To compare the risk of major adverse cardiovascula...
Article
Purpose To describe the prescribing trends of 17 therapeutic drug categories and the specific drug classes of systemic antibiotics, analgesics, and antidepressants in children and adolescents in the United Kingdom between 1998 and 2018. Methods A population-based retrospective cohort study including children and adolescents aged 0 to 18 years. Ove...
Preprint
Variable selection is commonly used to arrive at a parsimonious model when relating an outcome to high-dimensional covariates. Oftentimes a selection rule that prescribes the permissible variable combinations in the final model is desirable due to the inherent structural constraints among the candidate variables. Penalized regression methods can in...
Article
Full-text available
Our study aimed to describe levothyroxine prescription patterns and trends over time among pregnant women with subclinical hypothyroidism (SCH) in the United Kingdom. We used data from the Clinical Practice Research Datalink linked to its Pregnancy Register and the Hospital Episode Statistics database from 1998 to 2017. The study population include...
Article
Full-text available
The accelerated failure time model is an alternative to the Cox proportional hazards model in survival analysis. However, conclusions regarding the associations of prognostic factors with event times are valid only if the underlying modeling assumptions are met. In contrast to several flexible methods for relaxing the proportional hazards and linea...
Article
Background Several antihypertensive drugs are available for the primary prevention of cardiovascular disease (CVD). However, existing evidence on prescription patterns was primarily generated among patients at high CVD risk with short-term follow-up, and failed to capture impacts of time and patient characteristics. Our objective was therefore to d...
Article
In the statistical literature, a number of methods have been proposed to ensure valid inference about marginal effects of variables on a longitudinal outcome in settings with irregular monitoring times. However, the potential biases due to covariate‐driven monitoring times and confounding have rarely been considered simultaneously, and never in a s...
Preprint
Full-text available
In studying the marginal effect of antidepressants on body mass index using electronic health records data, we face several challenges. Patients' characteristics can affect the exposure (confounding) as well as the timing of routine visits (measurement process), and those characteristics may be altered following a visit which can create dependencie...
Article
Full-text available
Objective To establish the risk of major bleeding in direct oral anticoagulant (DOAC) users (overall and by class) versus vitamin K antagonist (VKA) users, using healthcare databases from four European countries and six provinces in Canada. Methods A retrospective cohort study was performed according to a similar protocol. First-users of VKAs or D...
Article
Aims: To describe changes in the utilization of basal insulins (glargine, detemir, degludec, neutral protamine Hagedorn [NPH]) among individuals with type 2 diabetes between 2003 and 2018 in the United Kingdom (UK). Materials and methods: Using the UK Clinical Practice Research Datalink (CPRD) Aurum, we created three study cohorts of individuals...
Article
Purpose: Researchers are interested in studying longitudinal patterns of gestational weight gain, yet this requires daily/weekly weights, and maternal weight is measured only during prenatal visits. We evaluated the relative accuracy and precision of methods for estimating maternal weight between prenatal visits among twin and singleton pregnancie...
Article
Epidemiologists sometimes use external sources of variation to explore highly-confounded exposure-outcome relationships or exposures that cannot be randomized. These exogenous sources of variation, or natural experiments, are sometimes proposed as instrumental variables to examine the effects of a given exposure(s) on a given outcome(s). Previous e...
Article
Background: In perinatal epidemiology, the development of risk prediction models is complicated by parity; how repeat pregnancies influence the predictive accuracy of models that include obstetrical history is unclear. Methods: To assess the influence of repeat pregnancies on the association between predictors and the outcomes, as well as the in...
Article
Full-text available
COVID-19 vaccines are now being deployed as essential tools in the public health response to the global SARS-CoV-2 pandemic. Pregnant individuals are a unique subgroup of the population with distinctive considerations regarding risk and benefit that extend beyond themselves to their fetus/newborn. As a complement to traditional pharmacovigilance an...
Article
Context: The efficacy and safety of metformin for obesity in children and adolescents remains unclear. Objective: To assess the efficacy and safety of metformin via systematic review. Data sources: Data sources included PubMed, Embase, the Cochrane Library, Scopus, and ClincalTrials.gov (inception to November 2019). Study selection: We selec...
Article
Background: A previous large randomized trial indicated that preconception-initiated low-dose aspirin (LDA) therapy did not have a positive effect on pregnancy outcomes. However, this trial was subject to nonadherence, which was not taken into account by the intention-to-treat approach. Objective: To estimate per protocol effects of preconceptio...
Article
Purpose: Sodium-glucose co-transporter 2 inhibitors (SGLT-2i) have been associated with an increased risk of genitourinary tract infections. Through similar biological mechanisms, they may also increase the risk of community-acquired pneumonia. Our objective was to compare the rate of hospitalization for community-acquired pneumonia (HCAP) with SGL...
Article
Introduction Ectopic pregnancy occurs in 1% to 2% of the all recognized pregnancies, yet half of women who have an ectopic pregnancy do not have any known risk factors. A potential but unstudied risk factor for ectopic pregnancy is benzodiazepine use, which could affect muscle contraction in the fallopian tube. Objectives and Approach We compared...
Article
Full-text available
Background Propensity score (PS) analyses are increasingly used in multiple sclerosis (MS) research, largely owing to the greater availability of large observational cohorts and registry databases. Objective To evaluate the use and quality of reporting of PS methods in the recent MS literature. Methods We searched the PubMed database for articles...
Article
Background: Observational healthcare data can be used for drug safety and effectiveness research. The use of inverse probability of treatment weights (IPW) reduces measured confounding under the assumption of accurate measurement of the outcome variable; however, many datasets suffer from systematic outcome misclassification. Methods: We introdu...
Article
Objective: To compare medication persistence of tofacitinib with persistence of injectable biological disease-modifying antirheumatic drugs (bDMARD) in patients with rheumatoid arthritis (RA). Methods: We performed a retrospective new-user cohort study of patients with RA in the IBM MarketScan Research Databases. New users of tofacitinib or bDMA...
Article
The accelerated failure time (AFT) model has been suggested as an alternative to the Cox proportional hazards model. However, a parametric AFT model requires the specification of an appropriate distribution for the event time, which is often difficult to identify in real‐life studies and may limit applications. A semiparametric AFT model was develo...
Article
Deriving valid confidence intervals for complex estimators is a challenging task in practice. Estimators of dynamic weighted survival modeling (DWSurv), a method to estimate an optimal dynamic treatment regime of censored outcomes, are asymptotically normal and consistent for their target parameters when at least a subset of the nuisance models is...
Article
In this tutorial, we focus on the problem of how to define and estimate treatment effects when some patients develop a contraindication and are thus ineligible to receive a treatment of interest during follow‐up. We first describe the concept of positivity, which is the requirement that all subjects in an analysis be eligible for all treatments of...
Article
Precision medicine is an approach to health care in which treatment decisions are tailored to patient-level information. Statistical methods for the estimation of dynamic treatment regimes (DTRs) allow to uncover a sequence of personalized treatment rules for patients with chronic diseases. Of particular interest is the identification of an optimal...
Article
Study question: Are women who fill a benzodiazepine prescription before conception at increased risk of ectopic pregnancy? Summary answer: Risk of ectopic pregnancy is 50% higher among women who fill a benzodiazepine prescription before conception. What is known already: Benzodiazepine use in pregnancy increases the risk of miscarriage, advers...
Article
Full-text available
Objectives To examine the relation between prenatal urinary phthalate metabolite concentrations and preterm birth (PTB).Methods The data were drawn from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a pan-Canadian cohort of 1857 pregnant women enrolled between 2008 and 2011. We quantified urinary concentrations of 7 phthala...
Article
Objective To compare the risk of ectopic pregnancy among women with and women without antidepressant prescriptions around conception and examine whether this risk differs by prepregnancy depression status. Methods We conducted a cohort study of all pregnancies between November 1, 2008, and September 30, 2015, identified in the nationwide (American...
Article
Background Hypertensive disorders of pregnancy (HDP) are associated with an increased risk of premature cardiovascular disease (CVD), but existing cardiovascular prediction models do not adequately capture risks in young women. We developed a model to predict the 10‐year risk of premature CVD and mortality among women who have HDP. Methods and Res...
Article
We address estimation of the marginal effect of a time‐varying binary treatment on a continuous longitudinal outcome in the context of observational studies using electronic health records, when the relationship of interest is confounded, mediated and further distorted by an informative visit process. We allow the longitudinal outcome to be recorde...
Article
Background: Approximately 25% of children with concussion have persistent postconcussive symptoms (PPCS) with resultant significant impacts on quality of life. Melatonin has significant neuroprotective properties, and promising preclinical data suggest its potential to improve outcomes after traumatic brain injury. We hypothesized that treatment w...
Article
Background: The association between acetaminophen use during pregnancy and the development of attention deficit hyperactivity disorder (ADHD) in the offspring may be due to bias. Objectives: The primary objective was to assess the role of potential unmeasured confounding in the estimation of the association between acetaminophen use during pregn...
Article
Sequences of treatments that adapt to a patient's changing condition over time are often needed for the management of chronic diseases. An adaptive treatment strategy (ATS) consists of personalized treatment rules to be applied through the course of a disease that input the patient's characteristics at the time of decision-making and output a recom...
Article
Background: Literature is divided regarding the risk of neonatal ventricular septal defect (VSD) associated with first trimester ondansetron use in pregnancy. Methods: We evaluated the risk of VSD associated with first trimester exposure to intravenous or oral ondansetron in 33 677 deliveries at Magee-Womens Hospital in Pittsburgh, PA (2006-2014...
Article
In their Letter to the Editor1, the authors asserted that biased and inconsistent studies were included in a meta‐analysis by Ripamonti et al.2 Let us clarify that in the cited paper2 we showed heterogeneity measures, but no pooled estimate has been calculated for any effect measure, exactly for the reason that included studies were, for different...
Article
Purpose: Inversed probability weighted (IPW) estimators are commonly used to adjust for time-fixed or time-varying confounders. However, in high-dimensional settings, including all identified confounders may result in unstable weights leading to higher variance. We aimed to develop a visualization tool demonstrating the impact of each confounder o...
Article
Full-text available
Background: Some people with rare diseases rely on peer-led support groups for disease-specific education and emotional and practical support. Systemic sclerosis (SSc), or scleroderma, is a rare autoimmune connective tissue disease. Many people with SSc cannot access support groups, and, when support groups exist, they may not be sustained due to...
Preprint
Full-text available
Background: Administrative health records (AHRs), which are generated primarily for management and billing purposes, are now widely used in drug safety and comparative effectiveness studies. The development of analytic methods for multi-site studies can benefit from the availability of simulated data, which do not require ethical approvals and data...
Preprint
Full-text available
Background: Administrative health records (AHRs), which are generated primarily for management and billing purposes, are now widely used in drug safety and comparative effectiveness studies. The development of analytic methods for multi-site studies can benefit from the availability of simulated data, which do not require ethical approvals and data...
Article
Background: We evaluated whether sample sizes in different arms of two-arm parallel group RCTs of non-regulated interventions were systematically closer in size than would plausibly occur by chance if simple randomization had been applied. Study design and setting: We searched PubMed for trials of non-regulated health care interventions that did...
Chapter
A distributed data network architecture allows sensitive individual‐level and institution‐level information to be stored locally under the direct control of participating data partners. It enables multidatabase comparative safety and effectiveness studies of rare exposures, rare outcomes, or specific patient populations, while providing strong prot...
Article
The U.S. Sentinel System and the Canadian Network for Observational Drug Effect Studies (CNODES) are two medical product safety surveillance networks. Using Sentinel’s pre‐programmed, parameterizable analytic tools, we reproduced two protocol‐based studies conducted by CNODES to assess the risks of acute pancreatitis and heart failure (HF) associat...
Article
Purpose: In distributed data networks, some data sites may be systematically missing important confounders that are captured by other sites in the network (eg, body mass index [BMI]). Multiple imputation may help repair bias in these scenarios. However, multiple imputation has not been described for distributed data networks where data access rest...
Article
Purpose: Little information is available on the performance of high-dimensional propensity scores (HDPS) in settings with more than two exposure levels. Our objective was to adapt the HDPS algorithm to allow for the inclusion of multilevel treatments and compare estimates obtained via this approach with those obtained via pairwise comparisons in a...
Article
The statistical study of precision medicine is concerned with dynamic treatment regimes (DTRs) in which treatment decisions are tailored to patient-level information. Individuals are followed through multiple stages of clinical intervention, and the goal is to perform inferences on the sequence of individualized treatment decision rules to be appli...
Article
Full-text available
Background: Chronic kidney disease (CKD) management focuses on limiting further renal injury, including avoiding nephrotoxic medications such as non-steroidal anti-inflammatory drugs (NSAIDs). We performed a systematic review to evaluate the prevalence of primary care NSAID prescribing in this population. Methods: We systematically searched MEDL...
Article
Full-text available
Postpartum complications can be life‐threatening, and predicting such complications would be useful to guide follow‐up of mothers through the postpartum period. Machine learning is an umbrella term referring to a suite of tools that can provide predictions in a range of settings. Betts et al (Betts BJOG 2019) use machine learning tools and routinel...
Article
Background: Women with a history of certain pregnancy complications are at higher risk for cardiovascular (CVD) disease. However, most clinical guidelines only recommend postpartum follow-up of those with a history of preeclampsia, gestational diabetes mellitus, or preterm birth. This systematic review was undertaken to determine if there is an as...
Article
Full-text available
Objective To determine whether use of dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists are associated with an increased risk of cholangiocarcinoma in adults with type 2 diabetes. Design Population based cohort study. Setting General practices contributing data to the UK Clinical Practice Research Dat...
Article
Full-text available
Background Meta‐analyses of observational studies have shown that women with a shorter interpregnancy interval (the time from delivery to start of a subsequent pregnancy) are more likely to experience adverse pregnancy outcomes, such as preterm delivery or small for gestational age birth, than women who space their births further apart. However, th...