SCATTER PLOT

If a researcher wishes to see whether a relationship exists between the number of hours studied and test scores in an exam, he must select a random sample of students, determine the hours each studied, and obtain their grades in the exam. A table can be made from the data.

The independent and dependent variables can be plotted on a graph called scatter plot. The independent variable, x, is plotted on the horizontal axis and the dependent variable, y, is plotted on the vertical axis.

Example 1.1 Construct a scatter plot for the data obtained in a study of age and systolic blood pressure for six randomly selected subjects.

Solution: Step 1 Draw and label the x and y axes.

               Step 2 Plot each point on the graph.

Example 1.2 Construct a scatter plot for the data obtained in a study on the number of absences and the final grades of seven randomly selected students from a statistics class.

Solution: Step 1 Draw and label the x and y axes.

               Step 2 Plot each point on the graph.

After the plot is drawn, it should be analyzed to determine which type of relationship, if any, exists.

• The plot shown in Example 1 suggests a positive relationship since the person’s age increases and blood pressure tends to increase also.
• The plot shown in Example 2 suggests a negative relationship since as the number of absences increases, the final grade decreases.

By: Andrea Beatrice Pechueco