Section 7.1 Scatter Plots & Best-Fitting Lines

Drawing a scatterplot Identify what your “x-values” (horizontal axis) and “y-values” (vertical axis) will be. Identify what your “x-values” (horizontal axis) and “y-values” (vertical axis) will be. Use the range of values to determine an appropriate scale for the axes. Use the range of values to determine an appropriate scale for the axes. Plot points. Plot points.

Best-fitting Lines A “line of best fit” is all about finding a line that seems to fit the general trend of points on a scatter plot. A “line of best fit” is all about finding a line that seems to fit the general trend of points on a scatter plot. Sometimes, a line fits very well, other times it doesn’t. This is where the CORRELATION, and CORRELATION COEFFICIENT comes in – they describe the trend of the data and whether it seems close to a line. Sometimes, a line fits very well, other times it doesn’t. This is where the CORRELATION, and CORRELATION COEFFICIENT comes in – they describe the trend of the data and whether it seems close to a line.

Two ways to describe correlation General terms: General terms: “positive correlation” “positive correlation” “negative correlation” “negative correlation” “no apparent correlation” “no apparent correlation” Correlation coefficient (an actual number) Correlation coefficient (an actual number)

Finding the line of best-fit There are several methods for finding “best-fit lines.” We’re going to look at three of those methods: visually estimating visually estimating Median-median line Median-median line Linear-regression line Linear-regression line

Visually estimating Here, we look at the data and guesstimate where the line should go. Then, we use two points on that line to find an equation.

Median-median line This one’s a little more complicated. Let’s check out the instruction sheet I gave you for this method alone! (PS – We’ll get to linear regression later….)

Let’s practice median-median lines Use the following data: (1, 22), (2, 27), (2, 20), (3, 15), (4, 19), (5, 10), (5, 14), (6, 9), (8, 7), (8, 11), (8, 13), (9, 5)

One more time!! (12, 42), (15, 72), (17, 81), (11, 95), (8, 98), (14, 78), (9, 83), (13, 87), (13, 92)