Standardized Testing & Psychometrics
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Assessment PrinciplesFree preview
Know What Kind of Score You Have
| Score | Typical metric | Key interpretation |
|---|---|---|
| Raw score | Number or points correct | Must usually be converted using the correct age table; not comparable across ages or tests |
| Standard score | Often mean 100, SD 15 | Equal-interval transformation locating performance relative to the normative group |
| Scaled score | Often mean 10, SD 3 | Common for subtests; verify the manual |
| z score | Mean 0, SD 1 | Number of standard deviations from the mean |
| T score | Mean 50, SD 10 | Transformation of a z score |
| Percentile rank | Percentage of norm group at or below the score | Ordinal; intervals are unequal |
| Age/grade equivalent | Median raw score for a comparison age/grade | Not an equal-interval score and not a diagnosis or instructional level |
High-Yield: A percentile rank of 25 does not mean 25% correct. The distance from the 5th to 10th percentile is not equivalent to the distance from the 50th to 55th.
The rest of this outline 7
- Reliability: Is the Measurement Consistent?
- Validity: Does the Evidence Support the Interpretation?
- Diagnostic Accuracy
- Norm-Referenced vs. Criterion-Referenced
- Fair, Defensible Assessment Decisions
- Common Traps
- Sources to Know
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