lecture_2_4,6 - Looking at data: relationships - Caution...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
    Looking at data: relationships Caution about correlation and regression The question of causation IPS chapters 2.4 and 2.6 © 2006 W. H. Freeman and Company
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Objectives (IPS chapters 2.4 and 2.5) Caution about correlation and regression The question of causation Residuals Outliers and influential points Lurking variables Association and causation
Background image of page 2
The distances from each point to the least-squares regression line give us potentially useful information about the contribution of individual data points to the overall pattern of scatter. These distances are called “residuals.” The sum of these residuals is always 0. Observed y Predicted ŷ residual ) ˆ ( dist. = - y y Residuals Points above the line have a positive residual. Points below the line have a negative residual.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Residuals are the distances between y -observed and y -predicted. We plot them in a residual plot. If residuals are scattered randomly around 0, chances are your data fit a linear model and you didn’t have outliers. Residual plots
Background image of page 4
The x -axis in a residual plot is the same as on the scatterplot. The line on both plots is the regression line. Only the y -axis is different.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Residuals are randomly scattered—good! Curved pattern—means the relationship
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 18

lecture_2_4,6 - Looking at data: relationships - Caution...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online