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- What we have here is six examples of possible surveys
- that might be conducted.
- What we want to do is critique them, see whether they're
- actually doing things that will give meaningful results,
- or results that you can actually make some
- judgment based on.
- So let's read the directions.
- It says, comment on the way the following samples have
- been chosen.
- For the unsatisfactory cases, suggest a way to improve the
- sample choice.
- All right.
- So A, you want to find whether wealthier people have more
- nutritious diets by interviewing people coming out
- of a five-star restaurant.
- So this is skewed on two directions.
- One, if you're only interviewing people out of a
- five-star restaurant, you're going to have a
- disproportionate number of wealthy people.
- And even the non-wealthy people who are eating at the
- five-star restaurant, they feel like they have enough
- money to eat there, so they're probably not that not-wealthy.
- They're probably pretty close to the threshold of wealthy.
- The other skew is that you're interviewing people at a
- restaurant, so you're disproportionately probably
- going to get people who eat out, as opposed to people who
- cook for themselves.
- And depending on whether this is a really healthy
- restaurant, maybe some type of organic, vegan, who knows
- what, restaurant, where you're going to get a
- disproportionate number of healthy people.
- Or maybe it's a really unhealthy restaurant.
- Maybe it's they put a lot of butter and sugar in the food.
- Who knows what it's all about?
- But this seems skewed on two dimensions.
- The best way to do it is, survey some proportion of
- wealthy people in an environment where it isn't
- being skewed by the type of food they eat.
- So you, once again, you wouldn't want to survey people
- at the organic grocery, because once again, you'd be
- skewing for people who maybe eat a little healthier.
- You'd want to do it maybe at some type of wealthy type of
- event, or something that's not food-oriented.
- I'd have to think more about what that might be.
- And you'd also want to survey people who are not wealthy, so
- at some other type of event where most of the population
- doesn't fall under the wealthy category.
- Or probably the best thing would be sampling people at an
- event that doesn't discriminate on wealth, and
- just surveying people and just ask them, in a broad bucket,
- do you make more than x?
- Whatever your definition of wealthy is.
- Or is your wealth, or is your income less than x?
- And then ask people what do they eat on a daily basis,
- something like that might work.
- So in general, I'm not a fan, not a fan.
- I don't think this passes mustards.
- It's biased on really two dimensions.
- B, you want to find out if there is a pedestrian crossing
- needed at a certain intersection by interviewing
- people walking by that intersection.
- So this is better than the first survey, but it still
- seems a little biased.
- And it depends how you define needed.
- Is needed if the people walking around the pedestrian
- crossing think it's needed, then this is OK.
- But if you want to objectively find out whether people in
- your community think it's needed, you want to have a
- broader sample.
- So you might want to also include drivers.
- Because obviously, the pedestrian crossing is going
- to affect them.
- You want to interview taxpayers in general.
- And obviously a lot of people might be all of the above.
- And you also might be missing pedestrians who would be
- walking by that intersection if there was a pedestrian
- crossing, but they're avoiding it, and so those are the
- people who would want it the most, but they're not even
- going to be there because they don't think that it's worth
- walking around there because you can't cross the street.
- So you're missing a whole sample of people.
- The best way I would do this is I would look within a,
- maybe a three block radius, or maybe a six block radius, of
- all of the homes and offices, and I would randomly survey a
- sample of those people.
- And I think that would be a better indication of whether
- the pedestrian crossing is needed.
- And actually, even a better way would be do
- it without a survey.
- You'd actually want to look at patterns of people walking and
- all of that, and compared to other things
- that might be needed.
- But this one definitely doesn't work for me.
- Now C, you want to find out if women talk more than men by
- interviewing an equal number of men and women.
- That seems reasonable.
- I guess if your survey, if you do it in a non-biased
- environment-- if you don't do it at, like, a business school
- or a law school where people might talk disproportionately,
- or it might be skewed towards women or men more.
- I don't know which way it would be skewed.
- But as long as you do it in a neutral place, and I guess
- their survey is, maybe they'll ask some arbitrary question.
- And they'll just time, or they'll count how many words
- the women talk versus the number of words the men talk.
- That seems like a reasonable way to see if women
- talk more than men.
- And once again, as long as you're not talking to some
- skewed sample, or biased sample, this
- seems pretty good.
- And it's good if it's an equal number.
- There's an equal number of men and women in the world.
- This seems to be-- I'll give it a smiley face right here.
- D, you want to find whether students in your school get
- too much homework by interviewing a stratified
- sample of students from each grade level.
- Well the first thing I want to do is, what is
- a stratified sample?
- And all that means is, you're going to sample people in the
- same proportion that they exist in the population.
- So let's say that your population-- your school--
- had, say they had 100 ninth graders.
- It has 200 tenth graders.
- 300 eleventh graders.
- And 400 twelfth graders.
- Actually, the school I attended actually, it went in
- the reverse order.
- I think we had like 800 ninth graders and 400 twelfth
- graders since so many people dropped out.
- But anyway, we don't have to be realistic here.
- So you had a total school population
- of about 1,000 students.
- So if you want to do a stratified sample, let's say
- you wanted to have a sample size of,
- let's say, 50 students.
- So you wanted to sample 50 students, and you wanted it to
- be a stratified sample.
- What that means is, you had 100 ninth graders out of 1,000
- in your school.
- So 10% of your school's population is ninth graders.
- So in your stratified sample, 10% also
- need to be ninth graders.
- So 10% of 5-- sorry-- 10% of 50 is 5.
- So you'd survey 5 ninth graders.
- In both situations, this is 10% of the population, it's
- going to be 10% of your sample.
- Likewise, you had 20% were tenth graders in the
- population, so 20% of your sample.
- Or 20% times 50 is 10 tenth graders should be surveyed.
- And then 30% of your school is eleventh graders, so 30% of
- your survey.
- So that should be 15 eleventh graders.
- And then finally 40% were twelfth graders.
- So in this situation, 40% of your survey, which is 20,
- should be twelfth graders.
- So that's all-- that's what a stratified sample means.
- Now let's talk about whether this is
- actually a good survey.
- You want to find out whether students in your school get
- too much homework, and you're interviewing
- students in your school.
- The one thing you definitely will find out is you will find
- out whether students in your school think-- think-- they
- think they get too much homework by interviewing a
- stratified sample.
- That would be true.
- That's what you would find out.
- Now, whether you could say that in a broader sense
- they're getting too much homework, you might want to
- include a larger audience, especially the other
- stakeholders in the whole homework doing process,
- especially parents and teachers.
- And actually a better way to do it would be, probably to
- compare the students in your school to a very similar
- school that has a different amount of homework, and maybe
- see the results on standardized tests.
- And you want to control.
- You want to make sure that there isn't a huge difference
- between the income levels, or the education levels of the
- kids' parents, and all that.
- I mean, it becomes much more involved.
- But this one still seems a little bit narrow, and all
- you're going to find out is whether students think they
- get too much homework.
- And I can almost guarantee you, they will think that they
- get too much homework, and so this survey might be a little
- bit of a waste of time.
- So I will put a frowny face.
- E, you want to find out whether there should be more
- public buses running during rush hour by interviewing
- people getting off the bus.
- So once again, what you're going to find out is whether
- people who ride, people getting off the bus think
- there should be more buses.
- So I won't write it here, but you're not going to find out
- objectively whether there should be more buses.
- Frankly, the best way to evaluate that, I think, is to
- just see how full, on average, the buses are.
- I would actually poll the actual buses and see how full
- they are during rush hour.
- If 90% of them are 100% full, or people can't get on a bus
- because they're full and that's happening frequently,
- and their total wait time is just getting ridiculous,
- that's probably a better assessment than
- just surveying people.
- But even beyond that, this is skewed on several levels.
- One, you are surveying only the people riding the bus.
- You're not surveying the other people in the community who
- might have an opinion on this: drivers, taxpayers who would
- have to pay for more buses.
- And then even within the bus-riding population, you
- have to think about when they're getting off the bus.
- If you're getting people off the bus during rush hour, I
- can almost guarantee you that they're going to say, yeah,
- we'd like more buses because then they would have less wait
- time, and the buses would be less crowded, and they
- wouldn't have to sit next to anybody.
- So even if it's not needed, they're going to say it is.
- But if you interview people maybe getting off the bus
- during lunchtime, who don't use the bus during rush hour,
- they might say no, we don't need more buses at rush hour.
- We need more at lunchtime.
- So you're going to get different answers depending on
- when the people are getting off the bus, and obviously,
- you're going to get very different answers from people
- not riding the bus.
- So if you want a broader audience, if you're kind of
- the city councilman trying to figure out what to do, I, once
- again, like the crosswalk, I would survey a random sample
- of people within three miles of the bus route, or
- something like that.
- I think that might be a better result.
- F, F-- I'll switch colors.
- You want to find out whether children should be allowed to
- listen to music while doing their homework by interviewing
- a stratified sample of male and female
- students in your school.
- Once again, stratified sample just means that, OK, if my
- school is 60% male, then 60% of my sample will be male.
- And that doesn't really seem relevant here.
- F seems very similar to the, do students think they get too
- much homework?
- Just as almost every student is going to say they get too
- much homework, almost every student should say they should
- be allowed to listen to music if they want to.
- And that's not going to be-- that's not really going to
- answer the question of whether children should be allowed.
- If you want a broader sample, you might-- just like the
- situation with the homework-- include
- parents and include teachers.
- But really, if you wanted to answer this question, the best
- way would actually be to look at, to survey students who
- listen to music while doing their homework, and students
- who don't listen to music while doing their homework,
- and see their relative grade performance, and that might
- give you a better answer.
- So once again, I think this one's a little weak.
- And the bus one was also a little weak.
- So the only good one here, if it's done right, is C.
- The other ones, they all needed a little bit of work to
- actually be surveys that would give meaningful information.