Researchers investigated whether a single cup of coffee improves short-term memory. They recruited $40$ graduate students and randomly assigned them to two groups. Group A drank a cup of coffee before performing a memory recall test, and Group B drank a decaffeinated placebo beverage. Each student completed the same recall test individually. The primary outcome was the number of words correctly recalled out of $30$. Identify the experimental units.

A nutrition study recorded body weight for $30$ participants before and after a $10$-week dietary program and reported the mean difference (after - before) in kilograms as $-3.75$ kg, with a standard deviation $1.92$ kg. What is the variable of interest, and is it qualitative or quantitative?

Which chart is NOT suitable for displaying qualitative data?

Recent annual revenue (in millions of dollars) for the leading music record labels is as follows:

Label A: 5300

Label B: 8900

Label C: 5800

Label D: 2500

Label E: 3100

Label F: 4200

Construct a Pareto chart to visualize the distribution of revenue. Are these data likely to be reasonably 

accurate?

Blank chart:

Which visualization would best show the proportion of market share held by four competing brands?

Researchers are studying the relationship between the finishing times of male and female runners in a marathon. Listed below are the finishing times (in minutes) of the top male and female runners from recent races. Construct a graph suitable for exploring an association between the finishing times of male and female runners. What does the graph suggest about that association?

Which of the following is an example of qualitative data?

A pie chart shows four regions: North (30%), South (25%), East (20%), West (25%). Which region has the largest share?

Which feature distinguishes a frequency polygon from a histogram?

Why is it incorrect to use a histogram to display eye color frequencies?