Research indicates self-disgust plays a significant role in the development and maintenance of depression, yet it is still a concept that is inadequately developed and often viewed as being only a single-faceted emotion. Although number of measures for assessing disgust have been developed, many of these give limited insight into notions of the self, focusing instead on external rather than internal matters. Hence, it is suggested that current tools to assess self-disgust are not sufficiently comprehensive. Thus, this thesis aims to develop a new scale of self-disgust that includes multiple aspects of the self. In this thesis, a new psychometric instrument, the Edinburgh Self-Disgust Scale (ESDS), is proposed to investigate self-disgust in both a clinical and non-clinical population in Saudi Arabia. Methods of translation and back translation are used, along with six instruments translated from English into Arabic. The first study aims to examine the psychometric properties (descriptive analysis, item-to-scale correlation, split-half reliability, internal consistency and confirmatory factor analysis) of the new questionnaire within a non-clinical sample. Confirmatory Factor Analysis (CFA) supports the division of the ESDS into five subscales (body shape, concept of the self, unacceptable behaviour, treatment of others and past-experience). External validity is confirmed through associations of subscales with existing measurements of factors relating to self-disgust: The Body Image Scale (BIS); the Multidimensional Self-Concept Scale, the Other as Shamer Scale (OAS), the Experience of Shame Scale (ESS), the UPPS-P Impulsive Behaviour Scale, the Self-Disgust Scale (SDS) and the Beck Depression Inventory – 2nd Edition (BDI-II). The results indicate that ESDS is significantly correlated with these measurements. The second study aims to replicate these findings using the clinical sample, to ensure that the ESDS behaves in a similar manner within a clinical population. Convergent validity with the BDI-II is also established. The ESDS is found to be significantly correlated with depression on the BDI and the existing factor structure is supported. It is concluded that the ESDS provides an appropriate and comprehensive assessment of self-disgust for an Arabic speaking population and shows convergent validity with the BDI-II in a clinical sample. Recommendations for future research and clinical utility are given.

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Family-based and genome-wide association studies (GWAS) of alcohol dependence (AD) have reported numerous associated variants. The clinical validity of these variants for predicting AD compared to family history has not yet been reported. These studies aim to explore the aggregate impact of multiple genetic variants with small effect sizes on risk prediction in order to provide a clinical interpretation of genetic contributions to AD. Data simulations showed that given AD’s prevalence and heritability, a risk prediction model incorporating all genetic contributions would have an area under the receiver operating characteristic curve (AUC) approaching 0.80, which is often a target AUC for screening. Adding additional environmental factors could increase the AUC to 0.95. Using the Collaborative Study on the Genetics of Alcoholism (COGA) and the Study of Addiction: Genes and Environment (SAGE) GWAS samples, we used several different sources to capture genetic information associated with AD in discovery samples, and then tested genetic sum scores created based on this information for predictive accuracy in validation samples. Scores were assessed separately for single nucleotide polymorphisms (SNPs) associated in candidate gene studies and in GWAS analyses. Candidate gene sum scores did not exhibit significant predictive accuracy, but SNPs meeting less stringent p-value thresholds in GWAS analyses did, ranging from mean estimates of 0.549 for SNPs meeting p<0.01 to 0.565 for SNPs meeting p<0.50. Variants associated with subtypes of AD showed that there is similarly modest and significant predictive ability for an externalizing subtype. Scores created based on all individual SNP effects in aggregate across the entire genome accounted for 0.46%-0.57% of the variance in AD symptom count, and have AUCs of 0.527 to 0.549. Additional covariates and environmental factors that are correlated with AD increased the AUC to 0.865. Family history was a better classifier of case-control status than genetic sum scores, with an AUC of 0.686 in COGA and 0.614 in SAGE. This project suggests that SNPs from candidate gene studies and genome-wide association studies currently have limited clinical validity, but there is potential for enhanced predictive ability with better detection of genetic factors contributing to AD.