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.

• Consider allowing students to use the four-step template from this lesson for a confidence interval. 

• After returning graded quizzes to students, consider showing them the 1-PropZInt on the TI 83/84 calculator or using the One sample z interval for a proportion applet at www.statsmedic.com/applets. 

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Common Student Errors

• When checking the Large Counts condition, students might state only np and n(1-p) must be greater than or equal to 10 without substituting any numbers. Insist that they show that the condition is met by plugging in values and confirming. 

• When finding a critical value z* for a 90% interval, students sometimes incorrectly look for an area of 0.10 in Table A, instead of looking for the correct area of 0.05 (90% of the area in the middle of the normal curve leaves 5% on either end). 

• When calculating the margin of error for a confidence interval for a proportion, students sometimes forget to multiply by the critical value z*.

• Students will sometimes skip parts of the 4-step process (like the specific formula). Insist that they show every part of the 4-step process.

• When determining the sample size needed for a specific margin of error, student sometimes round intermediate answers as they work towards an answer. Encourage them to store exact values on the calculator or keep all the numbers after the decimal.