AP Statistics Vocabulary 4.2

Observational Study

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

Experiment

deliberately imposes some treatment on individuals to measure their responses

Confounding

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

Treatment

is a specific condition applied to the individuals in an experiment. If an experiment has several explanatory variables, a treatment is a combination of specific values of these variables (also called factors).

Experimental Units

are the smallest collection of individuals to which treatments are applied. When the units are human beings, they often are called subjects

Random Assignment

in an experiment means that experimental units are assigned to treatments using a chance process. Doing so helps create roughly equivalent groups of experimental units by balancing the effects of other variables among the treatment groups.

Control

is the attempt to keep other variables that might affect the response the same for all group

Replication

Use enough experimental units in each group so that any differences in the effects of the treatments can be distinguished from chance differences between the groups.

Comparison

is using an experimental design that compares two or more treatments.

Control Group

is used to provide a baseline for comparing the effects of the other treatments.

Completely Randomized Design

has the experimental units assigned to the treatments completely by chance.

Statistically Significant

result occurs when the observed effect of an experiment is so large that it would rarely occur by chance.

Double-blind

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

Single-blind

if one party knows and the other does not.

Placebo

is the fake treatment given to control group in an experiment

Placebo Effect

occurs when some patients taking the placebo improve.

Randomized Block Design

A block is a 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. in a randomized block design, the random assignment of experimental units to the treatment is carried out separately within each block.

Matched Pairs Design

is a common form of blocking for comparing just two treatments. In some matched pairs designs, each subject receives both treatments in a random order. In others, two very similar subjects are paired, and the two treatments are randomly assigned within each pair.

Principles of Experimental Design

1. Comparison

2. Random assignment

3. Control

4. Replication