Browsing by Author "Lawal, Oluwaseyi Adetutu"

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    Measurement error in linear mixed models
    (2012) Lawal, Oluwaseyi Adetutu; Kim, Hyang Mi
    Measurement error of exposure is widely acknowledged as pervasive and often important source of bias or misleading results in much research. There has been an abundance of interest in the topic of covariate measurement error and there is an extensive literature in measurement error models and methods. Clustered data can be defined as data in which the observations are grouped into disjoint classes, called clusters, according to some classification criterion. Mixed models were developed to handle clustered data and have received a great deal of attention in the statistical literature for the past years because of the flexibility they offer in handling the unbalanced clustered data that arise in many areas of investigation. In this thesis we consider both linear and linear mixed effect models with measure­ment error. Three methods are compared through simulation studies, namely the naive method, the two-step approach, and the likelihood estimation method. The naive method ignores covariate measurement error in models, the regression calibration method, as a two-step approach, is a commonly used simple approach and may be applicable to al­most any regression models, and the Expectation Maximization (EM) algorithm, as a likelihood method, treats random effects as missing data. Naive approaches are shown to be inadequate to be used when covariates are subject to error. Both the regression calibration method and the EM method appear to be good, but the regression calibration method is much simpler than the EM method. We illustrate these methods in HIV study data.
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    Measurement Validity of the Seattle Angina Questionnaire in Coronary Artery Disease
    (2023-04-06) Lawal, Oluwaseyi Adetutu; Sajobi, Tolulope Timothy; Awosoga, Oluwagbohunmi Adetunji; James, Matthew Thomas; Santana, Maria Jose
    Patient-reported outcome measures (PROMs), such as the Seattle angina questionnaire (SAQ), are widely used to directly elicit perceptions of health status and quality of life (QOL) in individuals with coronary artery disease (CAD). The SAQ has been used in clinical and epidemiological studies to evaluate the effectiveness of treatment interventions, compare population groups, and inform quality improvement for CAD management. However, there is limited investigation of its measurement validity between groups and over time. The overarching goal of this research is to evaluate the validity of the SAQ in individuals with CAD between groups and over time. Specifically, the objectives are to (1) examine the factorial validity of the SAQ in a Canadian population of patients with CAD, (2) assess if the SAQ construct is equivalent across subgroups and over time and (3) test and adjust for response shift (RS) effect in the SAQ subscales over time. Data for this research were obtained from the Alberta Provincial Project on Outcome Assessment in Coronary Heart Disease (APPROACH) registry, a comprehensive, longitudinal inception cohort of all adult Canadians who received cardiac catheterization in Alberta, Canada. Exploratory and Confirmatory factor analysis (CFA) was used to investigate the underlying factor structure of the SAQ. CFA revealed that the factorial structure of the original 19-item SAQ, with five subscales, was inconsistent in this cohort. Instead, a 16-item Canadian version of this SAQ (SAQ-CAN), which includes four subscales, was found to be a better fit for the data and was a more valid and reliable instrument to measure QOL in CAD patients. Multigroup-CFA of the SAQ-CAN provides evidence supporting the equivalence of the underlying latent construct across sex, age, angina type, and treatment groups cross-sectionally and longitudinally in a sample of patients with CAD. Finally, the longitudinal structural equation model revealed the presence of small RS effects in the treatment-related experience subscale of the SAQ-CAN, which attenuated longitudinal changes on the SAQ-CAN subscales when not accounted for. In conclusion, this study proposes the use of SAQ-CAN as a valid and reliable instrument for assessing differences and temporal measures of QOL in individuals with CAD.