Quiz 1

Grace was curious if married people were more likely to be safe drivers than unmarried people. Grace took a random sample of car accident records from the past 555 years in her country, and she calculated what percent of accidents in the sample were caused by married people. She compared that result with the percentage of all drivers in the country that were married during that time period. What type of observational study is this?

A retrospective study

Annabella was curious about why people choose to skydive. She randomly selected 10 flights that were carrying skydivers and interviewed all of the skydivers on the flights about their motivations. What type of observational study is this?

A sample survey

First-year students at a certain large university are required to live on campus in 111 of the 242424 available residence halls. After their first year, students have the option to live away from campus, but many choose to continue living in the residence halls. Estella oversees 121212 of these residence halls. Her department surveyed a large simple random sample of first-year students who live in those 121212 residence halls about their overall satisfaction with campus living. Estella can safely generalize the results of the survey to which population?

All first-year students, but only those who live in these 12 residence halls

Angela created and maintains an exercise app where users log their workouts. She wonders if sending users a daily notification that reminds them to use the app will result in them logging more workouts. She releases an update to her app so that half of users will have daily notifications and the other half won't have daily notifications (randomly determined for each user). After a few weeks, she'll see if one group logs more workouts on average than the other group. What type of study is this, and what is the response variable?

An experiment where the number of workouts is the response variable

Before the 1936 US presidential election, a popular poll predicted that Alfred Landon would comfortably win against Franklin D. Roosevelt. The poll randomly sampled people from sources like telephone and car registration records, but the country was in an economic crisis, so many voters without those luxuries were not included in the poll. Voters with lower incomes favored Roosevelt, who ultimately won with 62%, percent of the vote—one of the largest margins of victory ever in a US presidential election.

Bias from undercoverage

A prestigious university wants to estimate the average starting salary of its graduates. The alumni outreach department sends an email to the most recent address they have on file for every graduate. The email asks the graduates to participate in a survey about their employment history and starting salary.

Current students are not included in the sample.

Valerie manages a team of 303030 employees at a large company. She wants to survey members of her team on her performance as their manager. She holds an individual meeting with each of her team's members and asks them the same set of questions. Valerie finds that 83%, percent of her employees rate her performance as "outstanding."

Employees may not want to give critical feedback in person to their manager, so this is likely an overestimate of Valerie's performance.

A popular online video game can be played on multiple platforms: video game consoles, personal computers, and mobile devices. The game offers 3 gameplay modes: solo, duo, and squad. Lee and Avery regularly play matches as teammates in duo mode on a video game console. They are curious how their average scores per match compare to other players. They use the game's website to take a large random sample of duo mode players on any platform. The sample has a mean of 585 points per match. For which population is 585 points a legitimate estimate of the average points per match?

Only duo mode players who play on any platform

A large city passed a new tax on sugary beverages. A few months after the tax goes into effect, the mayor wants to use social media to learn about how residents feel about the tax. The mayor creates a poll on Twitter and invites residents to share how they feel about the new tax. About 70%, percent of responses oppose the new tax. Which of these is the best explanation for why this result is probably biased?

Opponents of the new tax are more likely to respond than anyone else, so 70%, percent is likely an overestimate.

A high school has a policy that students' phones must be kept away during class. A principal used the school roster to poll a random sample of 50 students, and only 10%, percent said that they ever had their phone out during class. The next day, the principal observed classrooms and noticed that approximately 25%, percent of students had their phone out at some point during class. Which of these is the most concerning potential source of bias in the principal's poll?

Response bias

An airline wants to survey customers about their overall satisfaction. They take a random sample of 1{,}0001,0001, comma, 000 customers who have flown in the past month and email them a survey. The email also offers those who complete the survey a $25 gift card that can be used almost anywhere.

Satisfied customers might be less likely to complete the survey than dissatisfied customers.

A dentist wants to conduct a survey via telephone to determine what percent of all adults in their city floss daily. Which of these is the best example of response bias?

Some people might feel pressured to say they floss daily even though they don't.

A polling firm wants to contact a random sample of people likely to vote in an upcoming nation-wide election. They will use a random digit dialer to generate and call phone numbers at random, so the poll will include people with landlines, unlisted numbers, and mobile phones. The random digit dialer skips invalid phone numbers. If a person doesn't answer a call, the dialer will try one more time, and then skip that number. When a person does answer, a pollster asks a set of initial questions—such as the person's age and whether or not they voted in previous elections—to see if they are likely to vote in the upcoming election. If they are eligible and likely to vote, the pollster will then ask a series of questions about the election. Which of the following is not a potential source of bias in their poll?

The poll excludes people too young to vote.

Lucio wants to know whether the food he serves in his restaurant is within a safe range of temperatures. He randomly selects 70 entrees and measures their temperatures just before he serves them to his customers.

The population is all of the entrees Lucio serves; the sample is the 70 selected entrees.

The state Department of Transportation wants to know about out-of-state vehicles that pass over a toll bridge with several lanes. A camera installed over one lane of the bridge photographs the license plate of every tenth vehicle that passes through that lane. Identify the population and sample in this setting.

The population is all of the vehicles that pass through the lane with the camera; the sample is the group of every tenth vehicle that passes through the lane.