Simple Estimators of the Intensity of Seasonal Occurrence

Background: Edwards's method is a widely used approach for fitting a sine curve to a time-series of monthly frequencies. From this fitted curve, estimates of the seasonal intensity of occurrence (i.e., peak-to-low ratio of the fitted curve) can be generated. Methods: We discuss various approaches to the estimation of seasonal intensity assuming Edwards's periodic model, including maximum likelihood estimation (MLE), least squares, weighted least squares, and a new closed-form estimator based on a second-order moment statistic and non-transformed data. Through an extensive Monte Carlo simulation study, we compare the finite sample performance characteristics of the estimators discussed in this paper. Finally, all estimators and confidence interval procedures discussed are compared in a re-analysis of data on the seasonality of monocytic leukemia. Results: We find that Edwards's estimator is substantially biased, particularly for small numbers of events and very large or small amounts of seasonality. For the common setting of rare events and moderate seasonality, the new estimator proposed in this paper yields less finite sample bias and better mean squared error than either the MLE or weighted least squares. For large studies and strong seasonality, MLE or weighted least squares appears to be the optimal analytic method among those considered. Conclusion: Edwards's estimator of the seasonal relative risk can exhibit substantial finite sample bias. The alternative estimators considered in this paper should be preferred

Experimental and computational study of alkane dehydrogenation catalyzed by a carbazolide-based rhodium PNP pincer complex

A rhodium complex based on the bis-phosphine carbazolide pincer ligand was investigated in the context of alkane dehydrogenation and in comparison with its iridium analogue

Prevalent But Moderate Variation Across Small Geographic Regions in Patient Nonadherence to Evidence-based Preventive Therapies in Older Adults After Acute Myocardial Infarction

Patient long-term adherence to β-blockers, HMG-CoA reductase inhibitors (statins), and angiotensin-converting-enzyme inhibitors (ACEIs)/angiotensin receptor blockers (ARBs) after acute myocardial infarction (AMI) is alarmingly low. It is unclear how prevalent patient adherence may be across small geographic areas and whether this geographic prevalence may vary

Trends and Determinants of Oral Anti-Diabetic Initiation in Youth with Suspected Type 2 Diabetes

ObjectiveTo evaluate trends and identify predictors of treatment initiation of oral anti-diabetic drugs (OAD) in youth.Patients and MethodsWe identified a select population of children, ages 8–18 years, with at least 13 months of continuous health plan coverage within the years 2001–2012 in a large US commercial insurance claims database. New use of an OAD was defined as the first claim for an outpatient dispensing following a 12-month wash out period. Treatment incidence was estimated monthly over the study period, and stratified by age, gender, geographic region, and provider specialty.ResultsThe median size of the source population during the study period was 2.2 million children. A total of 13,824 initiators (mean monthly incidence of 4.6 (95% CI = 3.6, 5.5) per 100,000 youths) were identified. Initiators were more likely to be females, age 15–18, from the southern region, and have visited a family practitioner (versus a general pediatrician) prior to initiation. Time trends demonstrate a 43% increase in initiation from 2002–2012, with a gradual decrease starting from early 2008.ConclusionIncidence of filled OAD medications in youth increased over time, especially for patients treated by family practitioners. Additional research is needed into factors influencing prescribing by family practitioners and pediatricians

Estimation of biomarker distributions using laboratory data collected during routine delivery of medical care

To examine the extent to which commonly ordered laboratory values obtained from large health care databases are representative of the distribution of laboratory values from the general population as reflected in the National Health and Nutrition Examination Survey

Enrollment factors and bias of disease prevalence estimates in administrative claims data

Considerations for using administrative claims data in research have not been well-described. To increase awareness of how enrollment factors and insurance benefit use may contribute to observed estimates, we evaluated how differences in operational definitions of the cohort impacted estimates of disease prevalence

Statin initiation and acute kidney injury following elective cardiovascular surgery: a population cohort study in Denmark

OBJECTIVES: Acute kidney injury (AKI) is a serious complication of cardiac surgery. Statins may prevent post-surgical AKI, yet methodological concerns about existing studies raise questions about the magnitude of a protective effect. We sought to determine the effect of initiating a statin prior to elective cardiac surgery on post-surgical AKI in a regional Danish surgical cohort. METHODS: We identified adults who underwent cardiac surgery during 2006-11 using the Western Denmark Heart Registry. Presurgical medication use, pre- and post-surgical serum creatinine (sCr) measures, and other patient characteristics were obtained from Danish population-based registries. Post-surgical AKI was assessed using sCr measures within 5 days of surgery. The adjusted risk ratio (RR) of AKI and 95% confidence interval (CI) were estimated for patients who initiated a statin within 100 days prior to surgery compared with patients without prior statin use; long-term statin users were excluded to reduce healthy-user bias. Subanalyses were stratified by surgery type: coronary artery bypass grafting (CABG) and non-CABG surgeries. RESULTS: We identified 1929 CABG and 1775 non-CABG patients. AKI occurred in 25% of CABG and 28% of non-CABG surgeries, and in 29% of the non-users and 21% of the statin initiators. Half of CABG patients and 9% of non-CABG patients initiated a statin prior to surgery. The adjusted RRs for the effect of statin initiation on AKI were as follows: all surgeries combined, RR = 0.86 (95% CI: 0.74, 0.98); CABG, RR = 0.88 (0.74, 1.05); non-CABG RR = 0.87 (0.68, 1.11). CONCLUSIONS: Presurgical statin initiation is associated with a reduction in AKI risk after cardiac surgery

Identifying Specific Chemotherapeutic Agents in Medicare Data: A Validation Study

Large healthcare databases are increasingly used to examine the dissemination and benefits and harms of chemotherapy treatment in routine practice, particularly among patients excluded from trials (e.g., the elderly). Misclassification of chemotherapy could bias estimates of frequency and association, warranting an updated assessment

Placebo Adherence, Clinical Outcomes, and Mortality in the Womenʼs Health Initiative Randomized Hormone Therapy Trials

Medication adherence may be a proxy for healthy behaviors and other factors that affect outcomes. Prior studies of the association between placebo adherence and health outcomes have been limited primarily to men enrolled in clinical trials and cardiovascular disease outcomes. We examined associations between adherence to placebo and the risk of fracture, coronary heart disease, cancer, and all-cause mortality in the two Women’s Health Initiative (WHI) hormone therapy randomized trials

Population Trends by Predictor of Initiation- Age Group Specific Trends: Incidence per 100 000 Youth.

<p>Population Trends by Predictor of Initiation- Age Group Specific Trends: Incidence per 100 000 Youth.</p