AP Stats

observational study

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

experimental study

A study where treatments are deliberately imposed on individuals to observe their responses.

random sampling

A method of selecting samples in which each individual has an equal chance of being chosen.

response bias

Bias that occurs when respondents give inaccurate answers or when there is a flaw in the survey process.

internal validity

The extent to which a study demonstrates a causal relationship between intervention and outcome.

external validity

The extent to which results from a study can be generalized to and across settings, people, times, and measures.

control group

In an experiment, the group that does not receive the treatment or intervention.

placebo effect

The phenomenon where individuals experience a perceived improvement in their condition simply because they believe they are receiving treatment.

blocking

A technique used in experiments to reduce variability by grouping similar subjects together.

replication

The repetition of an experiment to confirm the results and increase reliability.

double-blind study

An experimental procedure in which both the participants and the researchers are unaware of which participants have received the treatment.

systematic sampling

A sampling method where you select every nth individual from a list.

stratified sampling

A sampling method that involves dividing the population into subgroups and taking random samples from each.

matched-pair design

An experimental design where pairs of subjects are matched in a way that they are similar except for the treatment.

mean

The average of a set of numerical values.

median

The middle value that separates the higher half from the lower half of a data set.

standard deviation

A measure of the amount of variation or dispersion in a set of values.

interquartile range (IQR)

The difference between the upper quartile (Q3) and lower quartile (Q1), representing the middle 50% of the data.

sampling distribution

The probability distribution of a given statistic based on a random sample.

normal distribution

A probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence.

confidence interval

A range of values, derived from a data set, that is believed to cover the true parameter with a specified probability.

hypothesis testing

A method of statistical inference used to decide whether the data at hand sufficiently support a particular hypothesis.

statistical significance

A determination of whether the observed effect in a study is likely due to chance.

type I error

The incorrect rejection of a true null hypothesis (false positive).

type II error

The failure to reject a false null hypothesis (false negative).

p-value

The probability of observing a statistic as extreme as, or more extreme than, the statistic observed, under the assumption that the null hypothesis is true.

null hypothesis

A statement that there is no effect or no difference, and it is the hypothesis that is tested.

alternative hypothesis

The hypothesis that there is an effect or a difference, contrary to the null hypothesis.

confounding variable

A factor other than the independent variable that might produce an effect in an experiment.

bias

A systematic error introduced into sampling or testing by selecting or encouraging one outcome or answer over others.

outlier

An observation that lies an abnormal distance from other values in the dataset.