Aim: Review for Exam Tomorrow

Independent VS. Dependent Variable

• Response Variables (DV) measures an outcome of a study

• Explanatory Variables (IV) explains or causes change in the response variables

Example: What is the IV and DV?Half of a group of third-graders was shown a film

on “sharing,” while the other half was not shown the film. The attitudes of the students in both groups towards sharing candy was then measured, and their mean scores were compared.

Examining Scatterplots– To examine scatterplots, need to:

1. Look at overall pattern and find deviations (outliers)2. Describe form (clusters), direction (+/- association)

and strength (weak/strong)Example: Describe relationship between variables.

Correlation Coefficient –Measures the strength of the linear relationship

between two variables 1 1r

2 22 2

n xy x yr

n x x n y y

R vs R-Squared

• r value of the correlation coefficient • Adjusted r square the relative predicted

power of a model between 0 and 1– 100% r square means perfect predictability (closer

to 1, the better)– Measure the quality of fit

Finding the equation of a regression line

• A regression line is also known as the line of best fit• Methods to finding an equation of the regression line:

or

a is the y intercept and b is the slope of the line

y a bx

2

22

22

y x x xya

n x x

n xy x yb

n x x

0 1y b b x

1

0 1

y

x

sb r

s

b y b x

Accuracy of Predictions?

• The accuracy of the prediction form a regression line depends on how much scatter about the line the data shows

• The regression line summarizes the pattern but gives only roughly accurate predictions