Biomedical subjects

Tulay Koru-Sengul

Publications and source records attributed to Tulay Koru-Sengul.

4 recordsLinked to original sources

PubMed2007

A residuals-based transition model for longitudinal analysis with estimation in the presence of missing data.

We propose a transition model for analysing data from complex longitudinal studies. Because missing values are practically unavoidable in large longitudinal studies, we also present a two-stage imputation method for handling general patterns of missing values on both the outcome and the covariates by combining multiple imputation with stochastic regression imputation. Our model is a time-varying auto-regression on the past innovations (residuals), and it can be used in cases where general dynamics must be taken into account, and where the model selection is important. The entire estimation process was carried out using available procedures in statistical packages such as SAS and S-PLUS. To illustrate the viability of the proposed model and the two-stage imputation method, we analyse data collected in an epidemiological study that focused on various factors relating to childhood growth. Finally, we present a simulation study to investigate the behaviour of our two-stage imputation procedure.

Bias↗

PubMed2006

How spiritual values and worship attendance relate to psychiatric disorders in the Canadian population.

OBJECTIVE: Research into risk and protective factors for psychiatric disorders may help reduce the burden of these conditions. Spirituality and religion are 2 such factors, but research remains limited. Using a representative national sample of respondents, this study examines the relation between worship frequency and the importance of spiritual values and DSM-IV psychiatric and substance use disorders. METHOD: In 2002, the Canadian Community Health Survey obtained data from about 37,000 individuals aged 15 years or older. While controlling for demographic characteristics, we determined odds ratios for lifetime, 1-year, and past psychiatric disorders, with worship frequency and spiritual values as predictors. RESULTS: Higher worship frequency was associated with lower odds of psychiatric disorders. In contrast, those who considered higher spiritual values important (in a search for meaning, in giving strength, and in understanding life's difficulties) had higher odds of most psychiatric disorders. CONCLUSION: This study confirms an association between higher worship frequency and lower odds of depression and it expands that finding to other psychiatric disorders. The association between spiritual values and mood, anxiety, and addictive disorders is complex and may reflect the use of spirituality to reframe life difficulties, including mental disorders.

Adolescent↗

PubMed2004

Estimating treatment effects from longitudinal clinical trial data with missing values: comparative analyses using different methods.

The selection of a method for estimating treatment effects in an intent-to-treat analysis from clinical trial data with missing values often depends on the field of practice. The last observation carried forward (LOCF) analysis assumes that the responses do not change after dropout. Such an assumption is often unrealistic. Analysis with completers only requires that missing values occur completely at random (MCAR). Ignorable maximum likelihood (IML) and multiple imputation (MI) methods require that data are missing at random (MAR). We applied these four methods to a randomized clinical trial comparing anti-depressant effects in an elderly depressed group of patients using a mixed model to describe the course of the treatment effects. Results from an explanatory approach showed a significant difference between the treatments using LOCF and IML methods. Statistical tests indicate violation of the MCAR assumption favoring the flexible IML and MI methods. IML and MI methods were repeated under the pragmatic approach, using data collected after termination of protocol treatment and compared with previously reported results using piecewise splines and rescue (treatment adjustment) pragmatic analysis. No significant treatment differences were found. We conclude that attention to the missing-data mechanism should be an integral part in analysis of clinical trial data.

Aged↗

PubMed2003

Comparison of in-hospital and one-year outcomes in patients with left ventricular ejection fractions or=50% having percutaneous coronary revascularization.

Outcome studies of percutaneous coronary intervention (PCI) with conventional balloon angioplasty have established increased in-hospital and 1-year mortality in patients with left ventricular (LV) dysfunction compared with others. It is unclear whether recent PCI practice innovations, including stents and adjunctive pharmacotherapy, have made PCI safer and more effective in patients with LV dysfunction. We evaluated the influence of LV ejection fraction (EF) indexes on in-hospital and 1-year outcomes in 1,458 patients within the National Heart, Lung, and Blood Institute-sponsored Dynamic Registry. Patients (n = 300) with acute myocardial infarction were excluded. The remaining 1,158 patients were subdivided into 3 categories: group 1, EF or=50% (n = 866). We determined the frequency of individual and composite adverse events (death/myocardial infarction [MI]/coronary artery bypass grafting) at discharge and 1 year. In the Dynamic Registry patients, mean EF in the 3 groups was 32%, 45%, and 62% and in-hospital mortality was 3.0%, 1.6%, and 0.1%, respectively (p <0.001). The composite end point of death/MI was also significant, but other in-hospital adverse events did not differ between groups. The respective mortality rates were 11.0%, 4.5%, and 1.9% (p <0.001) after 1 year. The composite end points of death/MI and death/MI/coronary artery bypass grafting also occurred more frequently in group 1 patients. Thus, significant LV dysfunction was still associated with increased in-hospital and 1-year mortality in patients having contemporary PCI.

Aged↗