Approaches to assessing the effectiveness of decision analyses in strategy development contexts have yet to be widely covered in the academic literature. In particular, there are two major gaps: first, a lack of conceptual links between socio-technical decision analysis and strategy development processes, and, second, a limited number of approaches that assess empirically the process effectiveness of decision analyses. This PhD research contributes to filling these gaps. The first part of this study analyses the contribution of socio-technical decision analysis to the effective development of strategies. I introduce a simplified taxonomy of strategy development that classifies socio-technical decision analysis as contributing both to enhanced information exchange ('socio' side) and improved information processing (technical side). The second part of the study assesses the effect of socio-technical decision analysis. I develop two measures to test the process effectiveness as well as the group alignment effects of the approach. An application to six case studies shows that socio-technical decision analysis is perceived as consistently more effective than existing decision processes on eight 'socio', technical and result-oriented dimensions. In addition, it has helped to create group alignment. The study also indicates that a group of relatively inexperienced decision analysts can apply socio-technical decision analysis successfully. The empirical studies, however, revealed several weaknesses in the approach, in particular on the information exchange side. The third part of the study addresses these weaknesses by introducing 'Strategy Conferencing'. The approach aims to enhance the effectiveness of socio-technical decision analysis in strategy development contexts by adding outside expertise to the process-based socio-technical decision analysis.