Chapter 4: How to Get a Good Sample

Question 1

sample survey

Answer 1

a subgroup of a large population is questioned on a set of topics. The results from the subgroup are used as if they were representative of the larger population, which they will be if the sample was chosen correctly.

Question 2

experiment

Answer 2

measures the effect of manipulating the environment in some way.

Question 3

randomized experiment

Answer 3

the manipulation is assigned to participants on a random basis.

Question 4

explanatory variable

Answer 4

the factor of an experiment being manipulated

Question 5

outcome variable/ response variable

Answer 5

the result of the explanatory variable

Question 6

observational study

Answer 6

resembles an experiment except that the manipulation occurs naturally rather than being imposed by the experimenter. For example, we can observe what happens to people’s weight when they quit smoking, but we can’t experimentally manipulate them to quit smoking.

Question 7

case-control study

Answer 7

A special type of observational study is frequently used in medical research that serves as a called a case-control study, it is an attempt to include an appropriate control group.

Question 8

meta-analysis

Answer 8

is a quantitative review of a collection of studies all done on a similar topic. Combining information from various researchers may result in the emergence of patterns or effects that weren’t conclusively available from the individual studies.

Question 9

case study

Answer 9

is an in-depth examination of one or a small number of individuals.

Question 10

unit

Answer 10

individual or object to be measured

Question 11

population/ universe

Answer 11

is the entire collection of units about which we would like information or the entire collection of measurements we
would have if we could measure the whole population.

Question 12

sample

Answer 12

sample is the collection of units we actually measure or the collection of measurements we actually obtain.

Question 13

sampling frame

Answer 13

is a list of units from which the sample is chosen.

Ideally, it includes the whole population.

Question 14

sample survey

Answer 14

measurements are taken on a subset, or sample, of

units from the population.

Question 15

census

Answer 15

a survey in which the entire population is measured

Question 16

margin of error

Answer 16

measure of accuracy in the form of a number. As a general rule, the amount by which the proportion obtained from the sample will differ from the true population proportion rarely exceeds 1 divided by the square root of the number in the sample. This is expressed by the simple formula 1/√n, where the letter n represents the number of people in the sample. To express results in terms of percentages instead of proportions, simply multiply everything by 100.

Question 17

probability sampling plans

Answer 17

sampling conditions where everyone in a population has a specified chance of making it into the sample

Question 18

simple random sample

Answer 18

sampling conditions in which every conceivable group of people of the required size has the same chance of being the selected sample.

Question 19

random numbers

Answer 19

Random numbers can be found in tables designed for that purpose, called “tables of random digits,” or they can be generated by computers and calculators.

Question 20

stratified random sample

Answer 20

sample is collected by first dividing the population of units
into groups (strata) and then taking a simple random sample from each

Question 21

strata

Answer 21

when a population of units falls into natural groups

Question 22

systematic sampling plan

Answer 22

With this plan, you divide the list into as many consecutive segments as you need, randomly choose a starting point in the first segment, then sample at that same point in each segment.

Question 23

random digit dialing

Answer 23

This method results in a sample that approximates a simple random sample of all households in the United States that have telephones. The method proceeds as follows. First, they make a list of all possible telephone exchanges, where the exchange consists of the area code and the next three
digits. Using numbers listed in the white pages, they can approximate the proportion of all households in the country that have each exchange. They then use a computer to generate a sample that has approximately those same proportions. Next, they use the same method to randomly sample banks within each exchange, where a bank
consists of the next two numbers. Phone companies assign numbers using banks so that certain banks are mainly assigned to businesses, certain ones are held for future
neighborhoods, and so on. Finally, to complete the number, the computer randomly generates two digits from 00 to 99.
Once a phone number has been determined, a well-conducted poll will make multiple attempts to reach someone at that household. Sometimes they will ask to
speak to a male because females are more likely to answer the phone and would thus be overrepresented.

Question 24

multistage sampling plan

Answer 24

Many large surveys, especially those that are conducted in person rather than over the telephone, use a combination of the methods we have discussed. They might stratify by region of the country; then stratify by urban, suburban, and rural; and then choose a random sample of communities within those strata. They would then divide those communities into city blocks or fixed areas, as clusters, and sample some of those. Everyone on the block or within the fixed area may then be sampled. This is called a multistage sampling plan.