Teacher resources and professional development across the curriculum

Teacher professional development and classroom resources across the curriculum

Session 3, Part A:
Organizing Data in a Stem and Leaf Plot (55 minutes)

In This Part:
How Long Is a Minute? | Making a Stem and Leaf Plot | Ordering a Stem and Leaf Plot
Interpreting the Stem and Leaf Plot | Grouping by Fives | Ordering Low and High

Let's begin with a problem you saw in Session 1, How Long Is a Minute?. You will use the data from this problem to create a stem and leaf plot, a useful device for organizing certain types of data. Note 1

As always, we begin with Step 1 of our four-step problem-solving process:

How good is your sense of time? Without a timing device, how well can you judge the actual length of a minute? Are some people better at judging elapsed time than others?

Twenty-six people tried this activity. At the end of what each person judged to be a minute, the actual time that had elapsed was recorded to the nearest second. The responses (in seconds) were as follows:

26 Responses to the Question

 63 67 79 75 57 72 52 89 39 59 55 68 66 86 70 52 60 64 42 54 56 82 57 65 59 33

Note that this is quantitative data, since the responses are numerical values. Time, however, is not obtained by counting as you did when you determined the number of raisins in a box. Time can be measured on a number line, and any point on the line is a possible point in time. The recorded times above were rounded off to the nearest second. But any positive real number is a possible measurement for time. In this way, time is a continuous variable, and data collected on this type of variable are called continuous data. This is in contrast to a discrete numerical variable (like the raisins), which is often obtained by counting and usually assumes only whole numbers as values.

Another example of a continuous variable is height, measured in centimeters. A person's height can be any positive number, even though the data are typically rounded off to the nearest centimeter.

Organizing continuous data, or discrete data with a great deal of variation, often requires that values be grouped.

Problem A1

Can you think of why a line plot might not be a useful way to illustrate this data set?

 Video Segment In this video segment, participants discuss why a line plot would not be a useful way to display the results of their statistical inquiry. They then discuss how grouping the data could provide them with more information. Watch this segment after completing Problem A1. What would a more useful graphical representation of the data look like? If you're using a VCR, you can find this segment on the session video approximately 2 minutes and 24 seconds after the Annenberg Media logo.

 Session 3: Index | Notes | Solutions | Video