Downloadable versions of this activity are available in the following formats:

(RTF format, PDF )

## Teacher’s notes

This activity allows students to determine whether or not a relationship exists between two variables. It also allows students to consider the importance of controlled variables in data analysis.

- The notion of controlled and uncontrolled (dependent) variables is important in this activity. Students should be able to describe how controlling certain variables affects the types of conclusions they can make about the data. Many people are tempted to make false generalizations about data without taking into consideration the effects of variables.
- It is important for the students to make a decision as to whether or not a relationship exists before they can draw a line of best fit, because a line of best fit would have no meaning if the students have determined that no relationship exists.
- There is a variety of correct answers for Part 3 b) since student responses can depend on the sample they have chosen.

### Other possible activities:

1. Discuss with your class positive and negative correlation

2. Discuss with your class the importance of controlling variables.

3. Ask your students what it means if the line of best fit for one of their graphs goes through the origin. Discuss the idea of extrapolation outside the range of the data.

4. Have your students find the equations of their lines.

5. Ask your students what the line of best fit represents. Ask them why all the data points are not located directly on the line.

6. Since the focus of this activity is on making decisions about relationships between data, have your students graph the data using computer technology, if possible.

**Note:** If you have access to analytical software such as Fathom, see also the lesson entitled “Data management activities using analytical software” under *Learning Activities, Grades 9 to 12*. The *Exploring linear functions* activity includes PowerPoint instructions on graphing using Fathom software.

*Contributed by**Florence**Glanfield**,**University** of**Saskatchewan.*