AP Stats Unit 2 Review

If the correlation coefficient, r = -1.0

• all the points on the scatterplot must fall exactly on a straight line with a positive slope.

• all the points on the scatterplot must fall exactly on a straight line with a negative slope.

• all the points on the scatterplot must fall exactly on a straight horizontal line.

• all the points on the scatterplot must fall exactly on a straight vertical line.

Answer explanation

r=-1.0 indicates a perfect negative correlation thus all points lie exactly on the straight line with a negative slope.

What is least-squares line used for?

• To make predictions

• To make the graph look pretty

• To connect the points

• To make it look like you know what you are doing

Students in a group of chess teams submitted data about hours of team practice and the number of matches the team won.  The graph shows the results of the data.  Based on the linear regression equation y = 3.52 + 3.14x, if a team practices 4.5 hours per week next year, which is the best prediction of the number of chess matches a team could expect to win?  

• about 24

• about 12

• about 8

• about 18

The following scatter plot shows the weights and lengths of some dinosaurs.  Which statement accurately describes the information?

• The information shows a positive correlation.  The weight of a dinosaur tends to increase according to its length.

• The information shows a negative correlation.  the weight of a dinosaur tends to decrease according to its length.

• The information shows no correlation.  The weight and length vary according to the type of dinosaur.

• The information shows no correlation.  The relationship between the weight and length of a dinosaur is uncertain.

Shown is a residual plot. Would a linear regression model of the data be most appropriate?

• YES

• NO

Shown is a residual plot. How many negative residuals are there?

• 5

• 1

• 3

• 9

What does the slope represent in this situation?

• The sloth runs 1 feet in 3 minutes

• The sloth runs 3 feet in 1 minute

• The sloth runs fast

• The sloth runs 6 feet in 1 minute

What is the best description of this relationship?

• Positive Linear Association

• Negative Linear Association

• Nonlinear Association

• No association

What effect(s) would removing this point have?

• The coefficient of determination (r^2) would increase.

• The y-intercept would decrease.

• The correlation coefficient (r) would get closer to -1.

• None of these.

Adrianna gathered data on different schools' winning percentages and the average yearly salary of their head coaches (in millions of dollars) in the years 2000-2011. She then created the following scatterplot and regression line. The fitted line has a y-intercept of 39. What is the best interpretation of this y-intercept?

• The model indicates that teams with coaches who had a salary of 0 million $ will average a winning percentage of 39%

• The average winning % was 39%.

• The average salary was 39 million dollars.

• On average, each 1 million dollar increase in salary was associated with a 39% increase in winning percentage.