Education in Doctor of Medicine programs has moved towards an emphasis on clinical competency, with entrustable professional activities providing a framework of learning objectives and outcomes to be assessed within the clinical environment. While the identification and structured definition of objectives and outcomes have evolved, many methods employed to assess clerkship students' clinical skills remain relatively unchanged. There is a paucity of medical education research applying advanced statistical design and analytic techniques to investigate the validity of clinical skills assessment. One robust statistical method, multitrait-multimethod matrix analysis, can be applied to investigate construct validity across multiple assessment instruments and settings. Four traits were operationalized to represent the construct of critical clinical skills (professionalism, data gathering, data synthesis, and data delivery). The traits were assessed using three methods (direct observations by faculty coaches, clinical workplace-based evaluations, and objective structured clinical examination type clinical practice examinations). The four traits and three methods were intercorrelated for the multitrait-multimethod matrix analysis. The results indicated reliability values in the adequate to good range across the three methods with the majority of the validity coefficients demonstrating statistical significance. The clearest evidence for convergent and divergent validity was with the professionalism trait. The correlations on the same method/different traits analyses indicated substantial method effect; particularly on clinical workplace-based assessments. The multitrait-multimethod matrix approach, currently underutilized in medical education, could be employed to explore validity evidence of complex constructs such as clinical skills. These results can inform faculty development programs to improve the reliability and validity of assessments within the clinical environment.