In addition to validity, there are two other key characteristics of measurement. Reliability means a repeated measure yields similar results with every repetition. Objectivity (inter-rater reliability) means a measure yields similar results when performed by different measurers. A measure may be reliable or objective and yet not be valid. Factors like learning, fatigue, and environmental changes may reduce reliability, and poor directions, bias, or lack of training may reduce objectivity. Good reliability and objectivity are evidence for valid measurement, but are not sufficient to ensure validity.