AP Stats Unit 3 - Collecting Data

census

Study that attempts to collect data from every individual in the population.

sample

Subset of individuals in the population from which we collect data.

population

In a statistical study, the entire group of individuals we want information about.

convenience sampling

Sample selected by taking from the population individuals that are easy to reach.

voluntary response

A bias that occurs when people choose to be in the sample by responding to a general invitation.

bias

When the design of a statistical study is very likely to underestimate or very likely to overestimate the value you want to know.

random sampling

Using a chance process to determine which members of a population are chosen for the sample. (general term)

simple random sample

Sample chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample.

stratified random sampling

Sample obtained by classifying the population into groups of similar individuals, then choosing a separate SRS in each group and combining these SRSs to form the sample.

cluster sampling

Sample obtained by classifying the population into heterogeneous groups of individuals and then performing an SRS to choose entire groups.

undercoverage

Occurs when some members of the population are less likely to be chosen or cannot be chosen in a sample.

nonresponse

Occurs when an individual chosen for the sample can't be contacted or refuses to participate.

wording of questions

An important influence on the answers given in a survey. Confusing or leading questions can introduce strong bias, and changes in wording can greatly change a survey's outcome.

response bias

Occurs when there is a consistent pattern of inaccurate responses to a survey question. This could be due to the role of the surveyor or the wording of a question.

observational study

Study that observes individuals and measures variables of interest but does not attempt to influence the responses.

confounding

When two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other.

experiment

A study in which researchers deliberately impose treatments on individuals to measure their responses.

placebo

A treatment that has no active ingredient but is otherwise like other treatments.

treatment

Specific condition applied to the individuals in an experiment.

experimental unit

The object to which a treatment is randomly assigned.

subjects

Experimental units that are human beings.

factor

Explanatory variable in an experiment.

level

Specific value of an explanatory variable (factor) in an experiment.

comparison

Experimental design principle. Use a design with multiple treatments.

control group

Experimental group whose primary purpose is to provide a baseline for comparing the effects of the other treatments.

placebo effect

Describes the fact that some subjects respond favorably to any treatment, even an inactive one.

double-blind

An experiment in which neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received.

single-blind

An experiment in which either the subjects or those who interact with them and measure the response variable, but not both, know which treatment a subject received.

random assignment

Experimental design principle. Use chance to assign experimental units to treatments.

control

Experimental design principle that mandates keeping other variables that might affect the response the same for all experimental units.

replication

Experimental design principle where each treatment is assigned to multiple experimental units

completely randomized design

Design in which the experimental units are assigned to the treatments completely by chance.

block

Group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response to the treatments.

randomized block design

Experimental design begun by forming groups consisting of individuals that are similar in some way that is important to the response. Treatments are then randomly assigned.

matched pairs design

Common form of blocking for comparing just two treatments.

sampling variability

The fact that different random samples of the same size from the same population produce different estimates.

inference

Drawing conclusions that go beyond the data at hand.

statistically significant

When the observed results of a study are too unusual to be explained by chance alone.

causation

Conclusion from the results of an experiment that the treatments are responsible for the difference in responses.

inference about a population

Conclusion about the larger population based on sample data. Requires that the individuals taking part in a study be randomly selected from the population of interest.