ShmoopTube

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Here's your AP stats shmoop du jour:

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Bill has decided to fulfill his lifelong dream and open an exotic yogurt store.

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He has narrowed his possible future location to one of two large cities and would like to determine the

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location with the most yogurt fanatics.

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Which of the following studies would be the best approach to finding his new location?

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And here are the possible answers...

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Okay. We know, we know, before we even get to the real question, the more important question...

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is it greek yogurt or frozen yogurt?

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Let's just say it's frozen yogurt because everybody loves some froyo in town.

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Back to the real question...The question asks us how Bill should measure the amount of yogurt

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fanaticism by area. To do this, we'll want a survey that measures how much people like

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yogurt in each of the two large cities.

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Emphasis on the word SURVEY.

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Since experiment E merely compares the how much people like exotic and standard yogurt by area

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and is an experiment..not a survey,

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we can rule out option (E) as an answer choice.

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The question also mentions that we're dealing with two large cities...so doing any kind

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of census where we poll every single person in the population...kind of like that government

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population census they do every 10 years...

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Too much money and time to do it...

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Bill needs as much time as possible to perfect his new shnozberry yogurt recipe.

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Therefore, we are left with three surveys: the mail-in survey, the grocery store survey,

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and the phone survey, options A, C, and D.

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Ok, the mail-in survey. First of all, if you

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ever saw a survey in the newspaper...when have you ever actually filled it out and turned

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it in? Besides...who reads newspapers anymore...

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Honestly, the only people who will turn in the mail-in

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survey are those feel really strongly..either positively or negatively..about establishing

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a new yogurt store in the area.

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Kind of like Bill.

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This kind of bias is called self-selection bias.

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The people being surveyed "self-select" themselves into the group that really cares

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about froyo.

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The local grocery store survey. Let's think about this. What if you just don't happen

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to shop at that particular grocery store that Bill's handing out surveys?

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Maybe you live too far, maybe you had a late night and couldn't get up to go with your parents to

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the store...Regardless, the local grocery store surveys won't give Bill a random sample

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of the city. It'll give him a sample of the people who happen to shop at the particular grocery store that day.

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And finally, we're left with option D. The phone survey.

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Oo, we like that word: random.

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Random is usually a good indicator in stats that you're performing the right type of experiment

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without sampling biases. The word stratified in this case

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just means that Bill is first

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dividing or stratifying the population into each of the two cities...and then choosing

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random people to survey in each group. Answer's (D).

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And since we like random things so much, we can't wait until Bill installs his new random

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yogurt flavor-making machine. The machine will mix up to three random flavors chosen

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from his exotic stock.

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Watch out for the anchovy yogurt, people.

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