Vocab Quiz 3B

Response Variable 

Measures an outcome of a study

Explanatory variable

may help explain or predict changes in a response variable 

Confounding

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

Placebo

a treatment that has no active ingredients but is otherwise like other treatments

Treament

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.

Experimental unit 

the object to which a treatment is randomly assigned. When the experimental units are human beings, they are often called subjects

Subjects

What the experimental unit is called when they are humans

Levels

The different values of a factor

Control group

used to provide a baseline for comparing the effects of other treatments. Depending on the purpose of the experiment, a control group may be given an inactive treatment (placebo), an active treatment, or no treatment at all.

Placebo effect

Describes the fact that some subjects in an experiment will respond favorably to any treatment even an inactive treatment.

Double-blind experiment

Neither the subjects nor those who interact with them and measure the response variable know which treatment a subject is receiving.

Single-blind experiment

either the subjects or the people who interact with them and measure the response variable don’t know which treatment a subject is receiving.

Random assignment

when treatments are assigned to experimental units (or experimental units are assigned to treatments) using a chance process.

Completely randomized design

the experimental units are assigned to the treatments completely at random

replication

giving each treatment to enough experimental units so that a difference in the effects of the treatments can be distinguished from chance variation due to the random assignment.

control

keeping other variables constant for all experimental units

Principles of Experimental design

Comparison, random assignment, replication, and control

Block

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.

Randomized block design

the random assignment of experimental units to treatments is carried out separately within each block.

Matched pairs design

a common experimental design for comparing two treatments that uses blocks of size 2. In some matched pairs designs, two very similar experimental units are paired and the two treatments are randomly assigned within each pair. In others, each experimental unit receives both treatments in a random order.

statistically significant

When an observed difference in responses between the groups in an experiment is so large that it is unlikely to be explained by chance variation in the random assignment

Factor

an explanatory variable that is manipulated and may cause a change in the response variable