Sampling/Experiments Flashcards
In a statistical study, what is the population?
What is the entire group of individuals about which we want information via statistical study?
In a statistical study, what is the sample?
What is the part of the population from which we actually collect information?
What are common types of bias?
Under-coverage
Nonresponse
Misleading Response
Interviewer Bias
Question Wording
Question Order
What is bias?
A flaw in a statistical study that causes it to systematically favor certain outcomes.
What is a convenience sample?
A sample selected by taking the members of the population that are easiest to reach.
What is a voluntary response sample?
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.
What is a simple random sample (SRS)?
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.
What is a stratified random sample?
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.
What is a placebo treatment?
A dummy treatment such as a pill that has no direct effect on an individual.
Placebo treatments are used on the control group.
In an experiment, what are the subjects?
A subject is an individual to whom or to which the treatments are applied.
In an experiment, what is an explanatory variable (sometimes referred to as a factor)?
A variable that may explain or influence changes in a response variable.
In an experiment, what is a treatment?
any specific experimental condition applied to the individuals, or subjects.
In an experiment, what is the control group?
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.
What is a randomized comparative experiment?
An experiment that uses both comparison of two or more treatments and random assignment of subjects to treatments.
In the context of experimentation, what is a completely randomized design?
Comparable to SRS–
All the subjects are allocated at random among all the treatments
What is the definition of statistical significance?
An observed effect so large that it would rarely occur by chance.
What are the three basic principles of experimental design?
- Control effects of lurking variables (often by comparison
- Randomize assignment of subjects to treatments
- Use enough subjects to reduce chance variation in the results
What is a double-blind experiment?
An experiment in which* neither the subjects nor the people who interact with them know which treatment each subject is receiving*
In the context of experimentation, what is a matched pairs design?
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.
In the context of experimentation, what is block design?
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.
