Comparing Box Plots:

What Can We Conclude About Different Data Sets

An advantage of box-and-whisker plots is their usefulness in comparing data sets. More than one box-and-whisker plot can be drawn for the number scale, which allows for the comparison of a variable by groups.

Example

Mr. Grammar has two English classes, one 7th grade and one 10th grade. Last week, his students complained they have too much homework to do, so Mr. Grammar decided to take a survey. He asked each student to log the total number of hours he/she studied for one week. Then, Mr. Grammar compiled the results.
The following box-and-whisker plots summarize his data.

Comparing the Data: What to Consider

  1. What is the median number of hours logged by seventh graders?
  2. What is the median number of hours logged by tenth graders?
  3. What is the interquartile range for seventh grade?
  4. What is the interquartile range for tenth grade?
  5. Which data set has the greatest upper extreme?

See the answers to these questions.

Conclusions

What can we conclude from these comparisons?

In general, tenth graders have more hours of homework per week than seventh graders have. For example, half of Mr. Grammar's tenth graders logged 4 to 11 hours of homework a week while 50% of seventh graders spent between 2 and 6 hours. The most hours reported by seventh graders was 11 hours; tenth graders reported spending a maximum of 15 hours.

Go on to matching

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