Mohammad Ehsanul Karim

Mohammad Ehsanul Karim
University of British Columbia - Vancouver | UBC · School of Population and Public Health

PhD

About

88
Publications
5,786
Reads
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734
Citations
Additional affiliations
August 2015 - present
McGill University
Position
  • PostDoc Position
Description
  • The Canadian Network for Observational Drug Effect Studies (CNODES)
September 2009 - January 2015
University of British Columbia - Vancouver
Position
  • Causal Inference with Observational Multiple Sclerosis Data
September 2008 - December 2008
University of British Columbia - Vancouver
Position
  • Teaching Undergraduate Course
Education
September 2009 - January 2015
September 2007 - August 2009

Publications

Publications (88)
Article
Full-text available
Longitudinal observational data are required to assess the association between exposure to β-interferon medications and disease progression among relapsing-remitting multiple sclerosis (MS) patients in the "real-world" clinical practice setting. Marginal structural Cox models (MSCMs) can provide distinct advantages over traditional approaches by al...
Article
Full-text available
http://www.bmj.com/content/347/bmj.f6651
Article
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Last Observation Carried Forward (LOCF) is an ad-hoc method, with known limitations. In recent years, several methods publications have used LOCF in estimating the per-protocol effect via inverse probability of adherence weighted (IPAW) model, when a time-varying factor is partially measured by the study design. We compare the statistical performan...
Article
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...
Article
Full-text available
Study objective SARS-CoV-2 represents an occupational risk to paramedics, who work in uncontrolled environments. We sought to identify the occupation-specific risk to paramedics by comparing their seroprevalence of SARS-CoV-2 infection-specific antibodies to that of blood donors in Canada. Methods In this prospective cohort study, we performed ser...
Preprint
Objective Emerging evidence indicates that longer SARS-CoV-2 vaccine dosing intervals results in an enhanced immune response. However, the optimal vaccine dosing interval for achieving maximum immunogenicity is unclear. Methods This study included samples from adult paramedics in Canada who received two doses of either BNT162b2 or mRNA-1273 vaccin...
Article
Purpose : To explore the rheumatoid arthritis (RA)-cardiovascular diseases (CVD) association in relative and absolute risk scales among US adults aged ≥20 years over time and the effect modification of the association by age. Methods : We analyzed aggregated data from all ten continuous National Health and Nutrition Examination Survey cycles. A sa...
Article
Full-text available
Among a cohort of adult paramedics in Canada, we investigated the performance of nucleocapsid (N) antibody detection (measured with a V-PLEX assay) to identify previous COVID-19 infections and compared differences among vaccinated and unvaccinated. Our data indicate that vaccinated and unvaccinated groups require different thresholds to achieve opt...
Article
Full-text available
Background: Two-stage least square [2SLS] and two-stage residual inclusion [2SRI] are popularly used instrumental variable (IV) methods to address medication nonadherence in pragmatic trials with point treatment settings. These methods require assumptions, e.g., exclusion restriction, although they are known to handle unmeasured confounding. The ne...
Article
Full-text available
Importance Initiation of injection drug use may be more frequent among people dispensed prescription opioid therapy for noncancer pain, potentially increasing the risk of hepatitis C virus (HCV) acquisition. Objective To assess the association between medically dispensed long-term prescription opioid therapy for noncancer pain and HCV seroconversi...
Article
Introduction Unmeasured confounding poses a serious threat to observational studies of post-TB health outcomes. E-values have been recently proposed as a method to assess the magnitude of unmeasured confounding necessary to nullify, or to render non-significant, relative effect estimates from observational studies. Methods We calculated E-values f...
Article
The optimal dosing interval for severe acute respiratory syndrome coronavirus 2 vaccines remains controversial. In this prospective study, we compared serology results of paramedics vaccinated with mRNA vaccines at the recommended short (17–28 days) vs long (42–49 days) interval. We found that a long dosing interval resulted in higher spike, recept...
Article
Full-text available
Objective To assess the association between long term prescription opioid treatment medically dispensed for non-cancer pain and the initiation of injection drug use (IDU) among individuals without a history of substance use. Design Retrospective cohort study. Setting Large administrative data source (containing information for about 1.7 million i...
Conference Paper
Full-text available
Introduction: The instrumental variable (IV)-based methods (e.g., two-stage least square [2SLS], two-stage residual inclusion [2SRI], and nonparametric causal bound [NPCB]) can be used to address non-adherence in pragmatic trials. These methods require assumptions, e.g., exclusion restriction, although they are known to handle unmeasured confoundin...
Article
Regular internet access is suggested to facilitate Comprehensive Correct HIV/AIDS Knowledge (CCAK). We assessed this association using the 2018 Nigeria Demographic Health Survey data, including 30,784 participants. CCAK was defined as knowing two primary HIV prevention methods, healthy-looking persons can have HIV, and rejecting two HIV misconcepti...
Article
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Purpose Much of the extant research on quality-of-life (QoL) in homelessness has focused narrowly on health-related QoL. Far less is known about broader subjective quality-of-life (SQoL). The purpose of this study was to examine levels and predictors of SQoL among homeless and vulnerably housed individuals in a 4-year longitudinal study. Methods D...
Article
Background Interruptions in healthcare services contribute to an elevated risk of overdose in the weeks following release from incarceration. This study examined the association of use of community healthcare with nonfatal and fatal overdose in the 30 days following release. Methods We conducted a retrospective cohort study using linked administra...
Poster
Although the treatments are randomly assigned at baseline for pragmatic trials, subjects may deviate from the protocol because of switching to other treatments, loss to follow-up due to side-effects. An additional issue arises when there is an infrequent measurement frequency of post-randomization prognostic factors. Inability to adjust for non-adh...
Article
Full-text available
Background Hepatitis C virus (HCV) causes life-threatening chronic infections. Implementation of novel, economical or widely available screening tools can help detect unidentified cases and facilitate their linkage to care. We investigated the relationship between chronic HCV infection and a potential complete blood count biomarker (the monocyte-to...
Article
Full-text available
Introduction Increasing evidence indicates that chronic hepatitis C virus (HCV) infection is associated with higher risk of diabetes. Previous studies showed ethnic disparities in the disease burden of diabetes, with increased risk in Asian population. We described the incidence of type 2 diabetes related to HCV infection and assessed the concurren...
Article
Purpose : To estimate the risk of tuberculosis (TB)-associated depression. A second aim was to estimate the extent to which any increased risk of depression among TB patients may be mediated by the length of hospital length stay (LOS) Methods : Retrospective cohort study of linked healthcare claims and public health surveillance data. Our primary...
Article
Background The attained power, calculated conditional on the realized allocation, of a clinical trial may differ from the expected power, obtained pre-randomization through averaging over all potential allocations that could be generated by the randomization algorithm (RA). For example, a two-arm trial using a RA that is expected to allocate 20 par...
Poster
The measurement frequency of post-randomization prognostic factors in pragmatic clinical trials is typically infrequent. The inverse probability of adherence weighting (IPAW) method has been shown to substantially reduce the per-protocol effect estimate’s bias if those unmeasured longitudinal values are imputed more frequently. Previous application...
Poster
Introduction: Instrumental variable (IV)-based methods (e.g., two-stage least square [2SLS], two-stage residual inclusion [2SRI], and nonparametric causal bound [NPCB]) can be used to address non-adherence in pragmatic trials. These methods require assumptions, e.g., exclusion restriction, although they are known to handle unmeasured confounding. I...
Article
Full-text available
Objective Depression is a highly-prevalent disorder among US adults and despite advancements in treatment options, prevalence rates are increasing. With the emerging recommendations of dietary interventions such as high fish intake come potential risks, for example, exposure to methylmercury (MeHg). Case reports and animal models have suggested a p...
Article
Participants in pragmatic clinical trials often partially adhere to treatment. However, to simplify the analysis, most studies dichotomize adherence (supposing that subjects received either full or no treatment), which can introduce biases in the results. For example, the popular approach of principal stratification is based on the concept that the...
Article
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Background The 2018 World Health Organization HIV guidelines were based on the results of a network meta-analysis (NMA) of published trials. This study employed individual patient-level data (IPD) and aggregate data (AgD) and meta-regression methods to assess the evidence supporting the WHO recommendations and whether they needed any refinements....
Article
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Background Current epidemiological evidence of post-TB airway disease is largely cross-sectional and derived from high-TB-incidence settings. We present the first cohort study of post-TB airway disease in a low-TB-incidence setting. Aims (1) analyze the risk of airway disease by respiratory TB, (2) assess potential unmeasured confounding between T...
Article
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Background The use of individual patient data (IPD) in network meta-analyses (NMA) is rapidly growing. This study aimed to determine, through simulations, the impact of select factors on the validity and precision of NMA estimates when combining IPD and aggregate data (AgD) relative to using AgD only. Methods Three analysis strategies were compare...
Article
Vitamin A deficiency (VAD) may cause anemia. The research aimed at evaluating the effect of Vitamin A supplementation (VAS) on hemoglobin (Hb) is, however, limited and, conclusions drawn from a few studies have been concluded inconsistently. In Bangladesh, the prevalence of childhood anemia is high, as well as the prevalence of VAD. Therefore, the...
Article
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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...
Poster
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Background: To address treatment nonadherence, many statistical methods are proposed: the naïve methods (e.g., intention-to-treat, naïve per-protocol, and as-treated), inverse probability-weighted per-protocol (IP-weighted PP), and instrumental variable (IV)-based methods (e.g., two-stage least square (2SLS), two-stage residual inclusion (2SRI), an...
Article
The beta-interferons are widely prescribed platform therapies for patients with multiple sclerosis (MS). We accessed a cohort of patients with relapsing onset MS from British Columbia, Canada (1995-2013) to examine the potential survival advantage associated with beta-interferon exposure using a marginal structural model. Accounting for potential t...
Article
Full-text available
Background To inform World Health Organization (WHO) global guidelines, we updated and expanded the evidence base to assess the comparative efficacy, tolerability, and safety of first-line antiretroviral therapy (ART) regimens. Methods We searched Embase, Medline and CENTRAL on 28 February 2020 to update the systematic literature review of clinica...
Article
Background: Despite Canada's universal health-care system, millions of Canadians experience unmet health-care needs (UHCN). People with mood disorders may be at higher risk of UHCN due to barriers such as stigma and gaps in health-care services. Aim: We aimed to examine the relationship between having a diagnosed mood disorder and experiencing U...
Article
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Introduction: Despite a recent meta-analysis including 31 randomised controlled trials comparing methadone and buprenorphine for the treatment of opioid use disorder, important knowledge gaps remain regarding the long-term effectiveness of different treatment modalities across individuals, including rigorously collected data on retention rates and...
Poster
- From the simulation, we found that the naïve PP, naïve AT, and IPCW methods prone to give biased estimates in the pragmatic trials. The naïve PP and AT estimates are biased due to non-random adherence, and the IPCW estimates can be biased due to the artificial censoring mechanism. - To address nonadherence in the pragmatic trials, we can use the...
Article
Full-text available
In veneer-drying facilities, controllers face many challenges to maintain desired parameters in the final product based on customer’s needs. The major challenge is setting process parameters to control the temperature and humidity within the various sections in the drying machine to obtain the desired properties of the final product. The regression...
Article
Objective To compare non-tuberculosis (non-TB)-cause mortality risk overall and cause-specific mortality risks within the immigrant population of British Columbia (BC) with and without TB diagnosis through time-dependent Cox regressions.Methods All people immigrating to BC during 1985–2015 (N = 1,030,873) were included with n = 2435 TB patients, an...
Article
Full-text available
Background: In a cross-sectional stepped-wedge trial with unequal cluster sizes, attained power in the trial depends on the realized allocation of the clusters. This attained power may differ from the expected power calculated using standard formulae by averaging the attained powers over all allocations the randomization algorithm can generate. We...
Poster
Full-text available
Pragmatic trials offer practical means of obtaining real-world evidence (RWE) to help improve decision-making in comparative effectiveness settings. Analyzing these trial data are, however, particularly challenging in the presence of incomplete adherence (e.g., due to treatment discontinuation/switching). A wide variety of statistical methods are p...
Article
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Study design: Protocol for a pragmatic randomized controlled trial (the Exercise guideline Promotion and Implementation in Chronic SCI [EPIC-SCI] Trial). Primary objectives: To test if home-/community-based exercise, prescribed according to the international SCI exercise guidelines, significantly reduces chronic bodily pain in adults with SCI....
Preprint
Full-text available
Background In a cross-sectional stepped-wedge trial with unequal cluster sizes, attained power in the trial depends on the realized allocation of the clusters. This attained power may differ from the expected power calculated using standard formulae by averaging the attained power over all allocations the randomization algorithm can generate. We in...
Preprint
Full-text available
Background In a cross-sectional stepped-wedge trial with unequal cluster sizes, attained power in the trial depends on the realized allocation of the clusters. This attained power may differ from the expected power calculated using standard formulae by averaging the attained powers over all allocations the randomization algorithm can generate. We i...
Article
The present study examined the association of residential instability with hospitalizations among homeless and vulnerably housed individuals over a 4-year time period. Survey data were linked to administrative records on hospitalizations. Specifically, we used data from the Health and Housing in Transition study, a prospective cohort study that tra...
Article
Full-text available
Background: Maternal and child mortality remain a global health concern despite different interventions that have been implemented to address this issue. Adequate antenatal care (ANC) is crucial in reducing maternal and neonatal morbidity and mortality. However, in Rwanda, there is still suboptimal utilization of ANC services. This study aims to a...
Article
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Abstract Health researchers are familiar with the concept of trial power, a number that prior to the start of a trial is intended to describe the probability that the results of the trial will correctly conclude that the intervention has an effect. Trial power, as calculated using standard software, is an expected power that arises from averaging h...
Article
Full-text available
The objective of this study was to examine longitudinal associations between perceived quality of living spaces and mental and physical health-related quality of life (HRQoL) among homeless and vulnerably housed individuals living in three Canadian cities. The Health and Housing in Transition (HHiT) study was a prospective cohort study conducted be...
Article
Objective: To disentangle the role of NSAIDs in the increased risk of CVD among OA patients. Methods: This longitudinal study was based on linked health administrative data (HAD) from British Columbia, Canada. From a population-based cohort of 720,055 British Columbians, we matched on age and sex to assemble 7,743 OA patients and 23,229 non-OA c...
Article
Full-text available
Rapid social, economic, and environmental changes in the northern territories of Canada have raised concerns about potentially increasing levels of chronic disease. This concern prompted us to compare multimorbidity prevalence in Canada between the territories and provinces. We analyzed Canadian Community Health Survey data for 2013/14. We defined...
Article
Background: Guidelines recommend nephrology referral for people with advanced non-dialysis-dependent chronic kidney disease, based mostly on survival benefits seen in retrospective studies of dialysis patients, which may not be generalizable to the broader population with chronic kidney disease. We aimed to examine the association between outpatie...
Article
en Consider assessing the evidence for an exposure variable and a disease variable being associated, when the true exposure variable is more costly to obtain than an error‐prone but nondifferential surrogate exposure variable. From a study design perspective, there are choices regarding the best use of limited resources. Should one acquire the true...
Article
Although machine learning is increasingly being applied to support clinical decision making, there is a significant gap in understanding what it is and how nurses should adopt it in practice. The purpose of this case study is to show how one application of machine learning may support nursing work and to discuss how nurses can contribute to improvi...
Article
Full-text available
Background Different methods to prevent contrast-associated acute kidney injury (CA-AKI) have been proposed in recent years. We performed a mixed treatment comparison to evaluate and rank suggested interventions. Methods A comprehensive Systematic review and a Bayesian network meta-analysis of randomised controlled trials was completed. Results we...
Poster
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Increasing evidence indicates that distress is an important mechanism through which chronic conditions affect health burden. However, the extent to which gender moderates this relationship remains unclear. Therefore, we examined the extent to which distress mediates the relationships between prevalent chronic conditions, and health burden, and whet...
Article
In this study, we contribute to the emerging scholarship at the intersection of crime and health by estimating the effect of serious offending on offenders’ health. By building on sociological stress research, we identify and adjust for the key life course processes that may intervene on the pathway from offending to health using a rich set of meas...
Article
Full-text available
In clustered survival analysis applications, researchers frequently fit frailty models using parametric and nonparametric approaches to obtain the estimates for the parameters associated with the survival model covariates and heterogeneity (frailty). Availability of the off- the-shelve implementations and freely available R software packages makes...
Article
Full-text available
Introduction Longitudinal studies ascertain exposure, covariates, and outcomes over time. For estimating treatment effect on mortality, ignoring the time-varying nature of an exposure may lead to immortal time bias. Time-dependent confounding that affects future treatment may bias the estimated effects. Differences in baseline prognosis between tre...
Conference Paper
Background Worldwide, osteoarthritis (OA) is a major musculoskeletal disorder. Recent research suggests that OA is an independent risk factor for cardiovascular disease (CVD).¹ The relationship is complicated because non-steroidal anti-inflammatory drugs (NSAIDs), a proven risk factor for CVD, are frequently used for the treatment of OA.² Researche...
Article
The use of retrospective healthcare claims datasets is frequently criticized for the lack of complete information on potential confounders. Utilizing patient's health status-related information from claims datasets as surrogates or proxies for mismeasured and unobserved confounders, the high-dimensional propensity score algorithm enables us to redu...
Article
Correct specification of the inverse probability weighting (IPW) model is necessary for consistent inference from a marginal structural Cox model (MSCM). In practical applications, researchers are typically unaware of the true specification of the weight model. Nonetheless, IPWs are commonly estimated using parametric models, such as the main-effec...
Article
The marginal structural Cox model (MSCM) estimates can be highly sensitive to weight-model misspecification. We assess the performance of various popular statistical learners, such as LASSO, support vector machines, CART, bagged CART, and boosted CART, in estimating MSCM weights. When weight-models are misspecified, we find that the weights compute...