Week 11 Quiz

An illustrative campus post reads: "Support for overnight hours jumped 20 percent in one year, so the library should open around the clock." Which claim is the conclusion?

Select one.

• The library should open around the clock during finals week
• Support for overnight hours jumped 20 percent in one year
• Support for overnight hours rose 10 percentage points in one year
• The random survey found 60 percent of students in favor this year

Which illustrative passage offers a number as a premise for a conclusion, rather than only reporting the number?

Select one.

• "This year's random survey found 60 percent of students in favor of overnight hours."
• "Last year's random survey found 200 of 400 students in favor of overnight hours."
• "Sales of the new item went from 2 units to 4 units, so the store should order more of it."
• "A test for the condition was given to 1,000 people at a community health fair."

As the course uses the term, what is a change in percentage points?

Select one.

• The change between two percents divided by the starting percent and multiplied by 100
• The plain difference between two percents, found by subtracting one from the other
• The share of a whole group that a sample of people represents out of every 100
• The chance of an outcome stated as a count out of a named base such as 1,000

The running question's illustrative random sample found 50 percent of students in favor last year and 60 percent this year. Which report states the change correctly?

Select one.

• Support rose 10 percent, which is a 20 percentage-point increase
• Support rose 20 percentage points, which is a 10 percent increase
• Support rose 10 percentage points, which is a 10 percent increase
• Support rose 10 percentage points, which is a 20 percent increase

In the illustrative risk pair, a risk rises from 2 in 1,000 to 3 in 1,000. Which statement gives the change both ways?

Select one.

• A 50 percent relative increase and 1 more case per 1,000 people
• A 1 percent relative increase and 50 more cases per 1,000 people
• A 33 percent relative increase and 1 more case per 1,000 people
• A 50 percent relative increase and 50 more cases per 1,000 people

An illustrative headline says that a habit "raises your risk of a rare illness by 50 percent" and gives no other number. What does a careful reader need before deciding how much the change matters?

Select one.

• Proof that the 50 percent was worked out by dividing by the new risk rather than the old
• A second headline that repeats the same 50 percent figure for a different habit or illness
• The starting risk out of a named base, such as how many in every 1,000 people
• The number of words the article uses to describe the habit and the illness

In the illustrative screening table, 1,000 people are tested for a condition that affects 1 in 100. The test detects 9 of the 10 who have it and wrongly flags 99 of the 990 who do not. How should the course state what a positive test means?

Select one.

• 9 of the 10 people who have the condition test positive
• 9 of the 108 people who test positive have the condition
• 99 of the 108 people who test positive have the condition
• 90 of every 100 people who test positive have the condition

In the illustrative screening table, why do the false positives outnumber the true positives even though the test catches most people who have the condition?

Select one.

• The test makes more mistakes on people who have the condition than on people who do not
• The 1,000 people tested were a biased sample drawn only from people who already felt ill
• Every positive test is equally likely to be true or false whatever the condition's base rate
• The condition is rare, so the 990 people without it produce more false alarms than the 10 with it

An illustrative ad's bar graph shows a rival brand's satisfaction rating of 50 and its own rating of 55, on a vertical axis that starts at 45. One bar is drawn twice as tall as the other. How large is the real difference?

Select one.

• A 100 percent difference, since one bar is drawn twice as tall as the other
• A 50 percent difference, since the bars are drawn 5 units and 10 units tall
• A 10 percent difference, since the gap of 5 is a tenth of the rival's 50
• A 5 percent difference, since the two ratings are 5 apart on the scale

An illustrative city crime map shows one unusual month with a spike in reports and leaves out the months before and after it. Which misleading-graph trick is this?

Select one.

• A truncated axis that starts above zero so bar heights no longer match values
• A cherry-picked time window that shows only the stretch that fits the story
• A stretched scale that spreads a small change over most of the graph's height
• A base rate left out of a screening test given to a large group of people