ap stats final

population

The entire group of individuals about which we want information.

sample

A subset of the population from which we collect information.

census

Collects data from the entire population.

convenience sample

Choosing individuals who are easiest to reach, not randomized.

voluntary response sampling

Allows people to choose to be in the sample by responding to a general invitation, often biased.

simple random sample (SRS)

Every group of n individuals in the population has an equal chance to be selected as the sample.

stratified random sample

Selects a sample by choosing an SRS from each stratum and combining SRS's into one overall sample.

cluster sample

Obtained by selecting all individuals within a randomly selected collection or group of individuals.

strata

Groups within a population that are homogeneous based on a relevant characteristic.

cluster

Groups within diverse populations that ideally represent the population on a smaller scale.

systematic random sample

Selects a sample from an ordered arrangement of the population by randomly selecting one of the first k individuals and choosing every kth individual thereafter.

bias

The systematic favoring of certain outcomes due to the method of collecting data.

sampling frame

A list of all individuals in the population.

nonresponse bias

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

undercoverage

Occurs when some groups in the population are left out of the sampling process.

observational study

Observes individuals and measures variables of interest without attempting to influence responses.

response bias

When participants provide inaccurate, false, or misleading answers due to various influences.

association

A relationship between two or more variables, not implying causation.

confounding variable

An outside factor that influences both the independent and dependent variable.

experiment

Imposes treatment on individuals to measure their responses.

treatment

A specific condition applied to the individuals in study.

factors

The explanatory variables being manipulated that may cause a change in the response variable.

levels

Different values of the factors applied in an experiment.

placebo

A treatment with no active ingredient, but is similar to other treatments.

single-blind study

Either the subjects or the researchers are unaware of who receives active treatment or placebo.

double-blind study

Neither the participant nor the researcher knows who received the treatment or placebo.

placebo effect

Experimental results caused by expectations alone.

control group

The group that does not receive the experimental treatment for comparison.

random assignment

Creates groups that are roughly equivalent at the beginning of an experiment.

statistical significance

A statistical statement of how likely an obtained result occurred by chance.

replication

Giving each treatment to enough experimental units to distinguish differences in treatment effects.

completely randomized design

Treatments are assigned to experimental units completely by chance.

randomized block design

Random assignment of experimental units to treatments carried out within each block.

matched pairs design

Pairs of subjects are matched on a characteristic and randomly assigned to groups.

inference

Using information from a sample to draw conclusions about the population.

sampling variability

The natural tendency of randomly drawn samples to differ from one another.

scope of inference

The extent to which conclusions can be made about the population.

frequency table

Summarizes one categorical variable using counts.

relative frequency table

Summarizes one categorical variable using percentages or proportions.

two-way table

A table containing counts for two categorical variables.

marginal relative frequency

The percent of individuals with a specific value for one categorical variable.

joint relative frequency

The percent of individuals that have specific values for two categorical variables.

conditional relative frequency

The percent of individuals with a specific value for one categorical variable among those who share a value of another variable.

mosaic plot

A modified segmented bar graph where the width of each rectangle is proportional to the number in that category.

SUCS

For describing distribution: Shape, Unusual values, Center, Spread.

stemplot

A graphical representation of a dataset that organizes and displays data while preserving original values.

5 number summary

Includes min, Q1, median, Q3, and max.

density curve

A model that describes the overall pattern of a distribution of a random variable.

DUFS

For describing correlation: Direction, Unusual values, Form, Strength.

high leverage points

Points with much larger or smaller x-values than other points in the dataset.

outliers (regression)

Points that do not follow the data pattern and have large residuals.

influential point

An extreme value whose removal drastically changes the slope, y-intercept, or correlation.

regression line (LSRL)

A linear equation represented as predicted y = a + bx.

power model

When logging both variables linearizes the data.

exponential model

When logging only the y-variable linearizes the data.

large counts condition

Using normal approximation when np>=10 and n(1-p)>=10.

central limit theorem

When the number of samples is ≥30, the sampling distribution of the sample mean is approximately normal.