BACKGROUND

• Results of previous studies of reliability of performance-based assessments administered on one occasion:

  • Task-sampling variability is a major source of measurement error.
  • Variability among raters is usually small.

• Occasion is a hidden source of error variance: when tests are administered on one occasion, task-variability is confounded with occasion-variability (Cronbach, Linn, Brennan, & Haertel, 1997)

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