AP Stats Collecting Data Section

Simple Random Sample (SRS)-Most common

random selected subset of population

all members in sample have equal chance of being selected

General process of creating a simple random sample

define population and label individuals

randomize

select members for sample

stratified random sample

splits population randomly into groups/strata based on shared traits

-randomly select samples from each group

cluster sampling

splits population into groups/clusters

randomly selects ENTIRE CLUSTERS to sample

systematic random sampling

select individuals at regular/set intervals

start at random point

(example-picking every 5th person on a class roster after starting at a random number)

bad sampling practices

convience sampling and volunary response sampling tend toe produce very biased results

undercoverage, nonresponse, response bias, wording of the question

observational study

observe and collect data without interfering with particiapnts

OPPOSITE OF AN EXPERIMENT

4 principles of experimental design

1)Comparison (at least between 2 groups)

2)Random assignment

3)Control (keep all other variables constant)

4)Replication

Level

specific value or category of a factor in an experiment

confounding

when another variable impacts the results= hard to determine true cause

randomized block designs

specific type of random assignment where subjects are divided into blocks/groups based on specific characteristics. each block is randomly assigned to a a treatment

matched pair designs

specific type of experimental design where subjects are paired based on specific characteristics. each pair is randomly assigned a treatment or ONE subject in each pair could be control