AP STATS VOCAB WK 1

Advantage of using a Stratified Random Sample Over an SRS

1) guarantees each STRATA is represented

2) Reduces variability in a SRS of same size

Experiments - Treatment?

Yes

Obervational Study - Treatment?

No

Does correlation imply causation?

-observational studies do NOT show causation

-only WELL-DESIGNED, CONTROLLED, EXPERIMENTS, shows CAUSATION (cause & effect)

Why use a control group?

1) Used to evaluate effectiveness of treatment

2) REDUCES effect of confounding variables

Response Bias

untruthful reponse due to the question being badly worded or uncomfortable to answer truthfully

Volunteer Response Bias

When those who choose to participate are the only ones participating because they feel very strongly one way or the other

Undercoverage Bias

Where a certain group of the population is left out due to difficulty of including them

Selection Bias

Where a certain group is overrepresented over others in the sample

Confounding Variable

An uncontrolled variable (outside factor) that is affecting the response variable in place of the explanatory variable

SRS (Simple Random Sample)

A sample where n individuals are selected from a population in a way that every possible combination of n individuals is equally likely. The best possible method.

Stratified Random Sample

A sample in which simple random samples are selected from each of several homogeneous subgroups of the population (Strata).

Systematic Random Sampling

A method of sampling in which sample elements are selected from a list or from sequential files, with every nth element being selected after the first element is selected randomly within the first interval

Cluster Sample

A probability sampling technique in which clusters of participants within the population of interest are selected at random, followed by data collection from all individuals in each cluster.

Census

An attempt to reach the whole population (sample whole population)

Convenience Sample

Selects individuals easiest to reach; improper way to sample, introduces bias

Randomization

-reduces bias

-Random Sample (RS): generalize conclustion to population

-Random Assignment(RA): cause & effect