Exam 4: How to Get a Good Sample

Which is better, a survey of 50,000 people who participated on an Internet web site, or a survey of 5,000 people where a computer was used to randomly choose the survey participants?

For Questions use the following narrative Narrative: Apartment complex Suppose you want to survey the opinions of the residents of an apartment complex.The complex contains 100 buildings, each with 8 units per building, for a total of 800 units.You decide to sample 160 of the units. -{Apartment complex narrative} Suppose you start at a random starting point, and select every 5th unit to be in your sample, until you sample 160 units.What sampling method did you use?

Suppose you have a herd of 100 cows and you need to select a simple random sample of 5 cows to test for a certain disease.You call the cows in for the evening, and pick the 5 that arrive first.Is this a simple random sample? Why or why not?

A (an) __________ study is an in-depth examination of one or a small number of individuals.

Suppose a random sample of people from your city found that 20% of the respondents own a cell phone, and the margin of error was 3%.In other words, you are confident that between 17% and 23% of all the people in your city own cell phones, based on this study.Suppose also that 1,000,000 people live in your city.Does this mean then that 200,000 people most likely own cell phones, plus or minus 30,000; or in other words, that between 170,000 and 230,000 people most likely own cell phones? (This was found by taking the results in percentage form and multiplying by the population size.)

For Questions use the following narrative Narrative: Boat show The annual Vacation & Boat Show in Columbus, Ohio offers four types of attractions: boats, fishing gear, outdoor equipment, and vacation planning services.Tickets sell for $6 per person, and children under 5 get in free.This year the show organizers want to find out which attraction was most popular, so they surveyed 100 people at random who attended the show, and asked them.The results showed that 67% of them liked the boats best. -{Boat show narrative} Specify the sample.

With a (an) __________ sample, every conceivable group of people of the required size has the same chance of being the selected sample.

What is the most important advantage of using a randomized experiment vs.an observational study, in terms of the statistical results?

Give three major advantages to using a (well designed and conducted) sample survey rather than a census.

Most of the national polling organizations in the United States now use a method of sampling where a computer determines which phone numbers to call, given information such as the possible phone number exchanges to use, and the proportion of households with each exchange.This sampling method is called __________.

When you read the results of a scientific study, which of the following should you do first?

Suppose you sampled 2,500 people for a marketing survey, but your boss thinks that you should have sampled more, say 4,000 people, because he says the results would have been much more accurate, even under the tight budget and time constraints on the company.Using statistics, how would you convince your boss to agree with you?

As the number of units in the sample increases, the margin of error __________.

Name one advantage that observational studies have over experiments.

Which of the following situations will produce the most accurate results?

If you come across a survey based on a haphazard, volunteer, or self-selected sample, you should __________ the results.

Which of the following news story excerpts describes the results of a meta-analysis?

With a random sample of 2,500 people, we usually get an estimate that is accurate to within what percent of the truth (using the general rule)?

Why might a researcher choose to conduct a stratified random sample over a simple random sample? Give two reasons.

If 1,000 surveys go out and 300 of them are returned, the nonresponse rate is __________ %.