1. UNIT 6 Lesson #3: Scatter Plots
April 28, 2011

2. Scatter plots are graphs that display two-variable data as a series of points.
Because there are 2 measured properties, we must decide which will be the dependent variable and which will be the independent variable. DEPENDENT VARIABLE: the property whose values rely upon, or change according to the independent variable. INDEPENDENT VARIABLE: the property that does not rely on anything.

3. The dependent variable is plotted along the y- axis (vertical axis)
The independent variable is plotted along the x-axis (horizontal axis)

4. Examples: Identify the dependent and the independent variable in each of the following:
a) The temperature of a cup of coffee since the time it was initially poured.
A: dependent = temperature of coffee
independent = time coffee was poured
b) A player's distance from the basketball hoop versus the percent of baskets sunk.
A: dependent = percent of baskets sunk
independent = distance from hoop

5. c) The extension/stretch of a spring in relation to the amount of mass suspended from the spring
A: dependent = extension of spring
independent = mass
d) The speed at which a car is traveling versus the stopping distance.
A: dependent = stopping distance
independent = speed of travel

6. Scatter plots offer a nice way of seeing whether or not a relationship exists between 2 properties or attributes.
- The relationship or lack of a relationship does not depend on the linearity (how straight of a line is created which the data is graphed), but rather upon how much or little one variable affects the other.

7. The relationship between two variables is known as the correlation, and it may be positive or negative.
If 2 sets of data have a positive correlation, then both variables are increasing together.
If 2 sets of data have a negative correlation, then one variable increases, as the other decreases.

8. EXAMPLES:
Positive Correlation

9. Negative Correlation
Time Spent Watching TV (hours)

10. Steps for creating a scatter plot:
1. Determine which variable is the dependent and which is the independent 2. Label your x axis with the independent variable and your y axis with the dependent variable. Make sure you include unit beside your labels. 3. Plot your points according to the coordinates given. You first plot the x coordinate and then move up or down to the y coordinate 4. Make sure you clearly plot your points. Sometimes it is easier to see if you put a little x-mark instead of a dot and include a title.