An analysis of the exclusion criteria used in observational pharmacoepidemiological studies

Pharmacoepidemiological Research on N-Nitrosodimethylamine-Contaminated Ranitidine Use and Long-Term Cancer Risk: A Population-Based Longitudinal Cohort Study

N-Nitrosodimethylamine (NDMA), a carcinogenic chemical, has recently been identified in ranitidine. We conducted a population-based study to explore ranitidine use and cancer emergence over time. Using the Taiwan National Health Insurance Research Database, a population-based cohort study was conducted. A total of 55,110 eligible patients who received ranitidine between January 2000 and December 2018 were enrolled in the treated cohort. We conducted a 1:1 propensity-score-matching procedure to match the ranitidine-treated group with the ranitidine-untreated group and famotidine controls for a longitudinal study. The association of ranitidine exposure with cancer outcomes was assessed. A multivariable Cox regression analysis that compared cancer risk with the untreated groups revealed that ranitidine increased the risk of liver (hazard ratio (HR): 1.22, 95% confidence interval (CI): 1.09-1.36, p < 0.001), lung (HR: 1.17, CI: 1.05-1.31, p = 0.005), gastric (HR: 1.26, CI: 1.05-1.52, p = 0.012), and pancreatic cancers (HR 1.35, CI: 1.03-1.77, p = 0.030). Our real-world observational study strongly supports the pathogenic role of NDMA contamination, given that long-term ranitidine use is associated with a higher likelihood of liver cancer development in ranitidine users compared with the control groups of non-ranitidine users treated with famotidine or proton-pump inhibitors.

New-user and prevalent-user designs and the definition of study time origin in pharmacoepidemiology: A review of reporting practices

BACKGROUND

Guidance reports for observational comparative effectiveness and drug safety research recommend implementing a new-user design whenever possible, since it reduces the risk of selection bias in exposure effect estimation compared to a prevalent-user design. The uptake of this guidance has not been studied extensively.

METHODS

We reviewed 89 observational effectiveness and safety cohort studies published in six pharmacoepidemiological journals in 2018 and 2019. We developed an extraction tool to assess how frequently new-user and prevalent-user designs were reported to be implemented. For studies that implemented a new-user design in both treatment arms, we extracted information about the extent to which the moment of meeting eligibility criteria, treatment initiation, and start of follow-up were reported to be aligned.

RESULTS

Of the 89 studies included, 40% reported implementing a new-user design for both the study exposure arm and the comparator arm, while 13% reported implementing a prevalent-user design in both arms. The moment of meeting eligibility criteria, treatment initiation, and start of follow-up were reported to be aligned in both treatment arms in 53% of studies that reported implementing a new-user design. We provided examples of studies that minimized the risk of introducing bias due to unclear definition of time origin in unexposed participants, immortal time, or a time lag.

CONCLUSIONS

Almost half of the included studies reported implementing a new-user design. Implications of misalignment of study design origin were difficult to assess because it would require explicit reporting of the target estimand in original studies. We recommend that the choice for a particular study time origin is explicitly motivated to enable assessment of validity of the study.

The relationship between a cirrhosis-specific comorbidity scoring system and healthcare utilization patterns

BACKGROUND AND AIM

Patients with liver cirrhosis are impacted by comorbidities that affect healthcare utilization and survival. The study objective was to assess the relationship between a cirrhosis-specific comorbidity scoring system (CirCom) and healthcare utilization among patients with cirrhosis.

METHODS

A retrospective cohort analysis was conducted using electronic medical records from a large academic-based healthcare network. Patients aged 18-90 years with at least one International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis code for cirrhosis (571.2/571.5) between 2009 and 2014, and at least 180 pre-index and 365 days of post-index electronic medical record data were included. Patients were assigned CirCom scores based on comorbidities observed at/before index cirrhosis diagnosis. All-cause/cirrhosis-specific outpatient/hospital utilization was assessed post-index diagnosis across 1 year. Predictors of utilization (age, sex, race, body mass index, etiology, Model for End-stage Liver Disease, and CirCom) were assessed using negative binomial and Poisson regression with robust standard errors.

RESULTS

A total of 957 patients were included. Healthcare utilization according to CirCom demonstrated a positive linear relationship for both all-cause outpatient/hospital utilization, but no relationship was evident for cirrhosis-specific utilization. Increased CirCom was associated with an increased risk of all-cause utilization for both outpatient (relative risk [RR]: 1.75; 95% confidence interval [CI]: 1.47-2.07) and hospital (RR: 1.71; 95% CI: 1.38-2.12) utilization. However, CirCom showed a statistically non-significant association for cirrhosis-specific outpatient (RR: 1.08; 95% CI: 0.91-1.29) and cirrhosis-specific hospital (RR: 0.87, 95% CI: 0.67-1.13) utilization.

CONCLUSIONS

CirCom failed to predict cirrhosis-specific healthcare utilization but did positively predict all-cause utilization for both outpatient and hospital services and therefore may be useful in risk assessment and management of cirrhosis.

Revisiting the washout period in the incident user study design: why 6-12 months may not be sufficient

AIMS

The purpose of this study was to describe how washout period duration affects the size and accuracy of retrospective incident user cohorts.

MATERIALS & METHODS

MarketScan commercial claims data from 2007 to 2010 were used and included adults with an antihyperlipidemic, antidiabetic or antidepressant claim in 2010. Incident user cohorts using 3-, 6-, 12-, 24- and 36-month washouts were created and changes in sample size and incident user misclassification were described.

RESULTS & CONCLUSION

The 6- and 12-month washouts excluded 75 and 85% of the samples, respectively. Half of subjects in the 6-month washout cohorts were actually prevalent users, and the 12-month washout period resulted in 30% misclassified. Using common washout periods of 6-12 months may insufficiently address prevalent user bias in large commercial claims databases.

Does design matter? Systematic evaluation of the impact of analytical choices on effect estimates in observational studies

BACKGROUND

Clinical studies that use observational databases, such as administrative claims and electronic health records, to evaluate the effects of medical products have become commonplace. These studies begin by selecting a particular study design, such as a case control, cohort, or self-controlled design, and different authors can and do choose different designs for the same clinical question. Furthermore, published papers invariably report the study design but do not discuss the rationale for the specific choice. Studies of the same clinical question with different designs, however, can generate different results, sometimes with strikingly different implications. Even within a specific study design, authors make many different analytic choices and these too can profoundly impact results. In this paper, we systematically study heterogeneity due to the type of study design and due to analytic choices within study design.

METHODS AND FINDINGS

We conducted our analysis in 10 observational healthcare databases but mostly present our results in the context of the GE Centricity EMR database, an electronic health record database containing data for 11.2 million lives. We considered the impact of three different study design choices on estimates of associations between bisphosphonates and four particular health outcomes for which there is no evidence of an association. We show that applying alternative study designs can yield discrepant results, in terms of direction and significance of association. We also highlight that while traditional univariate sensitivity analysis may not show substantial variation, systematic assessment of all analytical choices within a study design can yield inconsistent results ranging from statistically significant decreased risk to statistically significant increased risk. Our findings show that clinical studies using observational databases can be sensitive both to study design choices and to specific analytic choices within study design.

CONCLUSION

More attention is needed to consider how design choices may be impacting results and, when possible, investigators should examine a wide array of possible choices to confirm that significant findings are consistently identified.

Diagnostic accuracy studies of fine-needle aspiration show wide variation in reporting of study population characteristics: implications for external validity

CONTEXT

Study comparisons rest on the assessment of applicability or external validity. Population characteristics are an important component of external validity and, although there has been a heightened awareness of deficiencies in reporting in diagnostic test accuracy (DTA) studies, the reporting of populations in DTA studies has not been investigated.

OBJECTIVE

To assess the quality of reporting of population descriptions in DTA studies for fine-needle aspiration cytology (FNAC).

DESIGN

Literature survey of common population parameters and usage patterns in FNAC DTA studies. We randomly selected 20 FNAC DTA studies in 4 categories (salivary glands, lung, thyroid, and pancreas) and determined the frequency of parameter usage.

RESULTS

Studies showed considerable variability in reporting patterns. On average, studies reported 2 to 4 parameters to describe study populations. Age, sex, and lesion size were most frequently reported. Sixteen percent of studies did not provide any population description. Population parameters were used to describe the sample population more frequently than to describe the selection process (P = .001). There were significant differences in the number of parameters specified by anatomic site (P = .001). Only 21% of studies provided a flow diagram. Thirty-three percent of studies mentioned the target population.

CONCLUSIONS

Studies show considerable variability in the description of sample populations and the population selection process. Studies often fail to provide flow diagrams or to provide a clear statement of the research problem. There is considerable opportunity for studies to improve both descriptions of sample populations and the process used to select them.

The incident user design in comparative effectiveness research

Comparative effectiveness research includes cohort studies and registries of interventions. When investigators design such studies, how important is it to follow patients from the day they initiated treatment with the study interventions? Our article considers this question and related issues to start a dialogue on the value of the incident user design in comparative effectiveness research. By incident user design, we mean a study that sets the cohort's inception date according to patients' new use of an intervention. In contrast, most epidemiologic studies enroll patients who were currently or recently using an intervention when follow-up began. We take the incident user design as a reasonable default strategy because it reduces biases that can impact non-randomized studies, especially when investigators use healthcare databases. We review case studies where investigators have explored the consequences of designing a cohort study by restricting to incident users, but most of the discussion has been informed by expert opinion, not by systematic evidence.

Good research practices for comparative effectiveness research: approaches to mitigate bias and confounding in the design of nonrandomized studies of treatment effects using secondary data sources: the International Society for Pharmacoeconomics and Outcomes Research Good Research Practices for Retrospective Database Analysis Task Force Report--Part II

OBJECTIVES

The goal of comparative effectiveness analysis is to examine the relationship between two variables, treatment, or exposure and effectiveness or outcome. Unlike data obtained through randomized controlled trials, researchers face greater challenges with causal inference with observational studies. Recognizing these challenges, a task force was formed to develop a guidance document on methodological approaches to addresses these biases.

METHODS

The task force was commissioned and a Chair was selected by the International Society for Pharmacoeconomics and Outcomes Research Board of Directors in October 2007. This report, the second of three reported in this issue of the Journal, discusses the inherent biases when using secondary data sources for comparative effectiveness analysis and provides methodological recommendations to help mitigate these biases.

RESULTS

The task force report provides recommendations and tools for researchers to mitigate threats to validity from bias and confounding in measurement of exposure and outcome. Recommendations on design of study included: the need for data analysis plan with causal diagrams; detailed attention to classification bias in definition of exposure and clinical outcome; careful and appropriate use of restriction; extreme care to identify and control for confounding factors, including time-dependent confounding.

CONCLUSIONS

Design of nonrandomized studies of comparative effectiveness face several daunting issues, including measurement of exposure and outcome challenged by misclassification and confounding. Use of causal diagrams and restriction are two techniques that can improve the theoretical basis for analyzing treatment effects in study populations of more homogeneity, with reduced loss of generalizability.

Increasing levels of restriction in pharmacoepidemiologic database studies of elderly and comparison with randomized trial results

BACKGROUND

The goal of restricting study populations is to make patients more homogeneous regarding potential confounding factors and treatment effects and thereby achieve less biased effect estimates.

OBJECTIVES

This article describes increasing levels of restrictions for use in pharmacoepidemiology and examines to what extent they change rate ratio estimates and reduce bias in a study of statin treatment and 1-year mortality.

METHODS

: The study cohort was drawn from a population of seniors age 65 years and older enrolled in both Medicare and the Pennsylvania Pharmaceutical Assistance Contract for the Elderly (PACE) between 1995 and 2002. We identified all users of statins during the study period and assessed the time until death within 1 year. The following progressive restrictions were applied: (1) study incident drug users only, (2) choose a comparison group most similar to the intervention group, (3) exclude patients with contraindications, (4) exclude patients with low adherence, and (5) restrict to specific high-risk/low-risk subgroups represented in randomized trails (RCTs).

RESULTS

The basic cohort comprised 122,406 statin users, who were on average 78 years old and predominantly white (93%) and showed an unadjusted rate ratio of 0.32 for statin users. When all 5 restrictions were applied (N = 11,673), the unadjusted rate ratio had increased to 0.72. Multivariable Cox regression adjusted rate ratios increased from 0.62 [95% confidence interval (CI), 0.58-0.66] to 0.79 (95% CI, 0.60-1.03). However, after the first 3 restrictions the effect size changed little. The final estimate is similar to that obtained as a pooled estimate of 3 pravastatin RCTs in patients age 65 years and older. We argue that restrictions 1 through 4 compromised generalizability little.

CONCLUSIONS

In our example of a large database study, restricting to incident drug users, similar comparison groups, patients without contraindication, and to adherent patients was a practical strategy, which limited the effect of confounding, as these approaches yield results closer to those seen in RCTs.