Part one provides a literature review on the development of attitude theory in marketing research and addresses concerns regarding the effects of common method variance (CMV) in published studies based on the reasoned-action paradigm of consumer behavior and decision making. The results of a marker-variable analysis, logit analysis, and reanalysis of path estimates support the validity of self-report survey research designs. Part two employs a survey design to develop and validate a scale to measure a consumer s tendency to use a complex decision style (CDS) in conceptualizing and negotiating high-stakes decision situations. Drawing from literature on cognitive style theory and complexity science, a complex approach to decision making is characterized as being complexity-focused; decision makers tend to rely more heavily on strategies such as collaborating with others and integrating a variety of information. The CDS scale is also applied within a conceptual model of choice of elective healthcare treatment, specifically, women s decisions regarding the use of hormone therapy, commonly referred to as HRT.