The literature on issues of the reliability and validity of objective and performance assessments in vocational education and training was reviewed and synthesized to develop guidelines for procedures to enhance reliability and validity. The review established the following facts: (1) validity is determined largely through inferences made by both the task developers and users; (2) the assessor's intention is an essential component of validity; (3) although "authenticity" provides evidence of the face validity of workplace assessments, additional evidence of content, criterion, construct, and consequential validity is needed before assessments can be called valid; and (4) an assessment's reliability is an estimate of the measurement task's accuracy or precision as a measurement instrument. The method of gathering evidence and characteristics of the candidate were identified as common sources of error associated with both objective and performance assessment. The following additional sources of error were associated with performance assessment: characteristics of the assessor; context of the assessment; and range and complexity of the task(s). It was concluded that each of these sources of error must be controlled throughout the assessment and that establishing clear task specifications (including evidence to be collected and decision-making rules) will increase reliability. (Contains 60 references.) (MN)