3. Scatter Plots and Line of Best Fit

Scatter plots display the relationship between two numerical variables. Each point represents one pair of values (x, y).

Reading a scatter plot:

• The x-axis usually shows the independent variable.
• The y-axis shows the dependent variable.
• Each dot is one data point.

Association patterns:

• Positive association: as x increases, y tends to increase (points trend upward).
• Negative association: as x increases, y tends to decrease (points trend downward).
• No association: points show no clear pattern.

[missing figure: scatter_plot_study_hours]

Line of best fit (trend line): a straight line drawn through a scatter plot that best represents the overall pattern of the data. It can be used to estimate values and make predictions.

Example: if the line of best fit for hours studied (x) versus test score (y) is
\[ y = 5x + 60 \]
then a student who studies 6 hours would be predicted to score
\[ y = 5(6) + 60 = 90 \]

On the GED®, you will not need to calculate the equation of the line yourself, but you must be able to read a given equation, estimate values from a graph, and describe whether an association is positive, negative, or absent.