Underestimating costs in major public sector social infrastructure development projects is a highly contested and problematic issue. Several gaps exist in the identification of root causes of cost overruns. Behavioural science academics advocate political and psychological explanations as root causes for cost overruns against technical factors, such as errors and omissions by engineers, practitioners and scientists. Most studies in this field primarily concentrate on developed countries.

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... h some studies have been undertaken in developing countries, very little attention is given to the Small Island Developing States (SIDS). This paper presents a case study of public sector social housing construction programmes in a Caribbean SIDS to further understand the root causes of cost overruns. Primary and secondary data spanning across two different political cycles were collected to test the concepts of whether political influences or technical influences are the true root causes of cost overruns. It was found that political explanations based on the psycho-strategic concept are the leading sources of cost risks on the final estimated contract price. This study strengthens the argument and discusses how strategic decisions emanating from the political directorate outweigh and influence informed technical decisions formulated during the planning stages.