Overall Notes

• There is one version of this assessment provided in the Teacher Resources Materials (TRM). Use this assessment as-is or use it as a model to create your own. 

• If you are making your own assessment, consider using the test bank and the ExamView software.

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Common Student Errors

• When interpreting a percentile, students often say “in” the 80th percentile, rather than “at” the 80th percentile. This is worth making a note to them, but we still give them full credit.

• When calculating a z-score, students will sometimes input the numbers into the calculator incorrectly as 90 – 80 / 4 = 70, instead of (90 – 80) / 4 = 2.5.

• When interpreting a z-score, a response of “1.43 above the mean” is incorrect. A z-score is measuring the number of standard deviations above or below the mean.

• When interpreting a z-score, students sometimes forget to include a direction. A good interpretation should always state the number of standard deviations above or below the mean. 

• When adding or subtracting a constant to a set of quantitative data, students will often incorrectly add or subtract the constant from the standard deviation. Remember that a shift of the data to the left or right does not change any of the measures of variability.

• Students often confuse left and right skew. The direction of the skew is the direction the distribution is being pulled.