IT 223

Fall 2026

Craig Miller

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Weekly Notes

• Week 0
• Week 1
• Week 2
• Week 3
• Week 4

Assignments

• Assignment 1
• Assignment 2
• Assignment 3
• Assignment 4

Technical References

• Course text (OpenStax Statistics)
• OpenIntro Statistics
• R tutorial

Assignment 3
Working with Z Scores
Submit before 11:30 Sunday October 4

Overview

For this assignment, you will continue interpreting distributions and start the practice of calculating and interpreting z scores. You'll be working the usability scores (SUS) that we collected as a class.

Analysis tasks

1. Download usability ratings and run the usability.R script. You will see that the data frame has a col column and a finder column. For each of the col and finder vectors, do the following:
   1. Summarize the descriptive statistics including mean and standard deviation
   2. Create a boxplot and a histogram. Describe their distributions.
   3. How many values are within one standard deviation of the mean? Is this consistent with the empirical rule?
   4. How many values are within two standard deviations of the mean? Is this consistent with the empirical rule?
2. Z-score analysis: for each of the two data column, do the following:
   1. A score of 68 is considered an average SUS score. What proportion of the data is greater than 68?
   2. Calculate the z-score of 68 for this data column. What proportion of the data is expected to be greater than 68 based on its z-score?
   3. A score of 80 is considered a good SUS score. What proportion of the data is greater than 80?
   4. Calculate the z-score of 80 for this data column. What proportion of the data is expected to be greater than 80 based on its z-score?
   5. A score of 60 is considered a marginally fair SUS score. What proportion of the data is greater than 60?
   6. Calculate the z-score of 60 for this data column. What proportion of the data is expected to be greater than 60 based on its z-score?
   7. Summarize differences between actual proportions for these benchmarks and the proportions inferred from the z-score.
3. Compare the ratings across the two applications (COL vs. course finder). What observations or interpretations do you have?

Deliverable

Create word or pdf file that contains the following:

1. A summary statement of your experience completing this assignment. It should contain a major finding from the paragraph of the last task (not the whole paragraph). Place this summary statement at the top of your document.
2. Your clearly labeled answers to questions and problems
3. Any additional details or output that you would like to include or document but are too long to insert among your answers.

Grading

The assignment is worth 5 points. Full credit will be awarded to complete, accurate and well presented submissions. Points will be deducted for the following:

• Summary statements that do not reference concepts or details specific to the assignment
• Summary statements without meaningful experiences and explanations
• Incomplete answers
• Inaccuracies (possibly excepting minor ones)