Scatter diagrams, correlation and regression Quiz

1. A regression line is $y=3+2x$ for $x$ between 0 and 10. What is the best interpretation of 2?

• A. When $x=0$, $y=2$
• B. Each increase of 1 in $x$ is associated with an average increase of 2 in $y$
• C. $y$ is always twice $x$
• D. $x$ causes $y$ to double

2. Which estimate is least reliable? The data has $x$ from 10 to 50.

• A. $x=20$
• B. $x=35$
• C. $x=48$
• D. $x=80$

3. Points on a scatter diagram fall in two separate clusters. What is the best action?

• A. Ignore the clusters and fit one line
• B. Delete the smaller cluster
• C. Investigate what the groups are, and consider a line for each
• D. Conclude there is no correlation

4. Sales of sunglasses and of ice cream are strongly correlated. What is the most likely explanation?

• A. Sunglasses cause ice-cream sales
• B. Ice cream causes sunglasses sales
• C. The correlation is exactly zero
• D. Warm, sunny weather increases both

5. A regression line is $y=-5+4x$ for $x$ from 2 to 9. Why is the intercept not meaningful?

• A. $x=0$ is outside the data range and gives a negative $y$
• B. The gradient is positive
• C. The intercept is always meaningless
• D. $x$ cannot be 2