This paper presents preliminary findings from a project investigating the application of a multi-source measurement approach to the assessment of higher order competencies in the public service industry. The aim of the project was to develop and validate a strategy to synthesise multiple sources of evidence to inform judgements of workplace competence. The methodology adopted integrates developments in two fields of study, performance appraisals and psychometrics. The method encapsulates features of a 360-degree feedback model that is widely used in performance appraisals, in which ratings are obtained from a supervisor, peers, subordinates, clients, and the assessment candidate (self-assessment). Item response (Rasch) modelling techniques are employed that allow for the identification of the competence of the candidate, the difficulty of the assessment task, and the influence of the source of evidence (e.g. supervisor, peer or subordinate ratings). Instrument development and preliminary data analysis are discussed.