Sampling/Experiments

Question 1

In a statistical study, what is the population?

Answer 1

What is the entire group of individuals about which we want information via statistical study?

Question 2

In a statistical study, what is the sample?

Answer 2

What is the part of the population from which we actually collect information?

Question 3

What are common types of bias?

Answer 3

Under-coverage

Nonresponse

Misleading Response

Interviewer Bias

Question Wording

Question Order

Question 4

What is bias?

Answer 4

A flaw in a statistical study that causes it to systematically favor certain outcomes.

Question 5

What is a convenience sample?

Answer 5

A sample selected by taking the members of the population that are easiest to reach.

Question 6

What is a voluntary response sample?

Answer 6

A sample which consists of people who choose themselves by responding to a broad appeal.

Voluntary response samples are biased because people with strong opinions are most likely to respond.

Question 7

What is a simple random sample (SRS)?

Answer 7

A sample that consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected.

Question 8

What is a stratified random sample?

Answer 8

To produce this type of sample, first classify the population into groups of similar individuals (strata), then choose a separate SRS in each stratum and combine these SRSs to form the full sample.

Question 9

What is a placebo treatment?

Answer 9

A dummy treatment such as a pill that has no direct effect on an individual.

Placebo treatments are used on the control group.

Question 10

In an experiment, what are the subjects?

Answer 10

A subject is an individual to whom or to which the treatments are applied.

Question 11

In an experiment, what is an explanatory variable (sometimes referred to as a factor)?

Answer 11

A variable that may explain or influence changes in a response variable.

Question 12

In an experiment, what is a treatment?

Answer 12

any specific experimental condition applied to the individuals, or subjects.

Question 13

In an experiment, what is the control group?

Answer 13

A randomly selected group of subjects to whom or to which is applied a treatment whose outcome is already known, such as a placebo treatment.

Control groups are necessary to provide something against which to compare the results.

Question 14

What is a randomized comparative experiment?

Answer 14

An experiment that uses both comparison of two or more treatments and random assignment of subjects to treatments.

Question 15

In the context of experimentation, what is a completely randomized design?

Answer 15

Comparable to SRS–

All the subjects are allocated at random among all the treatments

Question 16

What is the definition of statistical significance?

Answer 16

An observed effect so large that it would rarely occur by chance.

Question 17

What are the three basic principles of experimental design?

Answer 17

1. Control effects of lurking variables (often by comparison
2. Randomize assignment of subjects to treatments
3. Use enough subjects to reduce chance variation in the results

Question 18

What is a double-blind experiment?

Answer 18

An experiment in which* neither the subjects nor the people who interact with them know which treatment each subject is receiving*

Question 19

In the context of experimentation, what is a matched pairs design?

Answer 19

Pairs of subjects are chosen that are as closely matched as possible. Chance is used to decide which subject in a pair gets the first treatment. The other subject in that pair gets the other treatment.

Allows comparison of just two treatments.

Question 20

In the context of experimentation, what is block design?

Answer 20

An experimental design in which random assignment of individuals to treatments is carried out separately within each of several groups (blocks) of individuals that are known before the experiment to be similar in some way that is expected to affect the response to the treatments.