Week 4 Quiz

A researcher asks whether penguins with longer flippers tend to weigh more. On a scatterplot of the 342 penguins, which variable is the explanatory variable, and where does it go?

Select one.

• Body mass, on the horizontal axis, because it is the variable being explained
• Flipper length, on the horizontal axis, because the question starts from it
• Flipper length, on the vertical axis, because it is measured first
• Body mass, on the vertical axis, because heavier birds cause longer flippers

For the 342 penguins, the scatterplot of flipper length (across) and body mass (up) shows points rising from lower left to upper right in a band that follows a straight line, and the correlation is r = 0.8712. Which description fits?

Select one.

• Weak, positive, and curved
• Strong, negative, and linear
• Moderate, positive, and clustered
• Strong, positive, and linear

The penguin flipper lengths run from 172 mm to 231 mm, and the correlation between flipper length and body mass is r = 0.8712. A field team rewrites every flipper length in centimeters, so the range becomes 17.2 cm to 23.1 cm. What happens to the correlation?

Select one.

• It is divided by 10 as well
• It changes sign, because the numbers got smaller
• It stays the same, because r has no units
• It can no longer be computed until both variables share a unit

A board game scores each die face x by its squared distance from 3.5, so faces 1, 2, 3, 4, 5, 6 score 6.25, 2.25, 0.25, 0.25, 2.25, 6.25. The six points form a perfect U shape, and the correlation is 0. What does that correlation of 0 tell you?

Select one.

• There is no straight-line relationship, even though the score depends completely on the face
• The face and the score are unrelated
• The scores were computed incorrectly, because a perfect pattern must have r = 1
• The relationship is weak, so the face only slightly affects the score

A biologist wants two graphs from the penguin field log: one that shows the distribution of flipper length on its own, and one that shows how flipper length relates to body mass. Which pair of graphs fits?

Select one.

• A pie chart of flipper length, then a bar chart of both variables
• A histogram of flipper length, then a scatterplot of flipper length and body mass
• A scatterplot of flipper length, then a histogram of both variables together
• A bar chart of flipper length, then a two-way table of both variables

The species-by-island table shows 168 penguins on Biscoe: 44 Adelie and 124 Gentoo. Among the Biscoe penguins, what percentage are Gentoo? Round to one decimal and enter the number only.

Type a short answer.

The 344 penguins in the field log were seen on three islands: 168 on Biscoe, 124 on Dream, and 52 on Torgersen. In the marginal distribution of island, about what percentage of the penguins were seen on Biscoe?

Select one.

• 36.0%
• 73.8%
• 15.1%
• 48.8%

Select every statement about the correlation coefficient r that is true.

Select every option that applies.

• It always lies between negative one and positive one
• It has no units
• One unusual point can change it a lot
• An r of 0.8712 means 87% of the penguins follow the pattern
• It can be computed for species and island to measure their association

The Palmer penguins field log is an observational study: researchers measured the birds and assigned nothing. Flipper length and body mass have a correlation of r = 0.8712. Which conclusion is justified?

Select one.

• Longer flippers cause penguins to gain weight, because r is close to 1
• Heavier bodies cause flippers to grow, because the association is positive
• The two are strongly associated, but the data cannot show that one causes the other
• There is no real relationship, because the study was not an experiment

In children, shoe size and reading level tend to rise together. True or false: age is a lurking variable that could produce this association without bigger feet causing better reading.

True or false.

• True
• False