Method comparison studies consist of a unique study design aiming to examine agreement between two methods to measure a physiological or clinical parameter evaluated using continuous variables. Such physiological parameters are used by healthcare providers along with other clinical data to inform diagnoses and treatment decisions. When novel methods are proposed to measure a continuous physiological parameter, method comparison studies are needed to examine the agreement between this new method and an existing method that is used in standard clinical care. This standard method is generally considered as the gold standard measurement for a given physiological parameter. The issue of repeated measurements poses special challenges when conducting method comparison studies. Repeated measurements occur when a given individual included in a method comparison study has multiple measurements, which are inherently correlated with one another and are not independent (e.g., multiple glucose measurements carried out for the same patient throughout the day using a blood test, compared to a portable point-of-care device). The limits of agreement (LOA) method proposed by Bland & Altman has been adapted to adjust for the correlation between repeated measurements and is widely used for the analysis of method comparison studies that include repeated measurements. However, other statistical methods have been proposed as alternatives to LOA analysis to inform the analysis of method comparison studies with repeated measurements. There is a gap in the literature to inform this type of analysis, whereby no guidelines or synthesis of statistical methods that can be used as alternatives to the LOA method with repeated measurements have been published. Therefore, this thesis aimed to systematically review the existing literature to identify existing alternate statistical methods for the analysis of method comparison studies that include repeated measurements, using a scoping review framework. The findings of this scoping review were used to inform the analysis of the PREMISE (Point-of-care hemoglobin accuracy and transfusion outcomes in non-cardiac surgery) study, a large prospective observational method comparison study that included repeated measurements. The aim of the PREMISE study was to examine the agreement between frequently used point-of-care devices to measure hemoglobin (POCT-Hgb) and laboratory-measured hemoglobin (lab-Hgb) in the operative setting. To further increase the understanding of the challenges associated with the analysis of method comparison studies that include repeated measurements, the analyses pertaining to agreement were performed in the context of this thesis. The findings of the PREMISE study fill an important gap in the literature pertaining to transfusion decision-making in the operative setting, where there is a paucity of evidence on the accuracy of POCT-Hgb devices, as well as from trials and transfusion guideline.

The purpose of the present programme was to develop and validate a theoretically-grounded instrument to measure the planned and unplanned dimensions of lifestyle PA (PPA and UPA; Dunn, Andersen, & Jakicic, 1998). In Study 1, two samples of British adults (Internet: N = 742; paper: N = 563) were used to establish the content validity of the Brunel Lifestyle Physical Activity Questionnaire (BLPAQ). Exploratory factor analysis yielded a two-factor model (UPA and PPA) that produced acceptable fit indices using confirmatory factors analyses with both samples. The purpose of Study 2 was to examine the test-retest reliability of the BLPAQ over 5 weeks using a sample of leisure centre users, university staff members, and university students (N = 337). High correlations were observed between the two administrations (range = .93-.98; p < .01). Thereafter, the data were subjected to proportion of agreement (PoA) analysis as advocated by Nevill, Lane, Kilgor, Bowes, and Whyte (2001). Both PPA and UPA demonstrated satisfactorily high internal agreement (PoA > 95%). In Study 3, the BLPAQ was cross-validated using two criterion measures: the Baecke Questionnaire of Habitual Physical Activity (Baecke, Burema, & Frijters, 1982) and the Godin’s Leisure-Time Exercise Questionnaire (Godin & Shephard, 1985). Multiple linear regressions were performed to predict PPA and UPA from the subscales of the two reference measures. The predictive models differed markedly in terms of gender. Subsequently, the sample of 338 British adults was divided into two subsamples, and these were subjected to a cross-validation using the Limits of Agreement (LoA) methodology advocated by Bland and Altman (1986). The agreement plots revealed that both BLPAQ subscales demonstrated acceptable inter-sample agreement when compared to the criterion measures. In Study 4, a series of structural equation models were tested with the aim of predicting PPA and UPA using the variables that constitute the Theory of Planned Behaviour (TPB). The TPB was able to predict PPA but not UPA. The addition of a direct path between past behaviour to UPA did not result in a significant prediction. Further work is required to examine the factorial structure of the PPA subscale and to increase the number of items in the UPA subscale. In sum, the programme has contributed a valid and reliable theory-based measure of PA as well as evidence to support the utility of the TPB in PA research. However, the TPB framework may require the addition of predictors such as past behaviour and actual behavioural control.

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