Designing Experiments Section 5.2

Experimental Units Individuals on which the experiment is done If the individuals are human then we call them subjects

Treatment A specific experimental condition applied to the units (subjects)

Factors Explanatory variables in an experiment

Note: Experiments can give good evidence for causation They allow specific factors to be studied They study the combined effects of several factors

Placebo Effect Response to a dummy treatment

Control Group Group that receives the placebo

Principles of Experimental Design Control Randomize Replicate

Statistically Significant An observed effect so large it would rarely occur by chance

Completely Randomized When all experimental units are allocated at random among all treatments

Cautions About Experimentation

Lack of Realism Subjects, treatments, or setting of an experiment may not realistically duplicate the conditions

Double-blind Experiment Neither the subjects nor the people who have contact with them know which treatment a subject received

Randomized Comparative Experiment One of the most important ideas in statistics Able to give convincing evidence for causation

Matched Pairs Design Compares 2 treatments Blocks of 2 units that are as closely matched as possible Randomize the order for each subject Example of block designs

Block A group of experimental units or subjects that are known before the experiment to be similar in some way that is expected to affect the response to the treatments A form of control

Block Design Random assignment of units to treatments is carried out separately within each block Matched pairs is a form of block design

Practice Problems pg. 306 #5.49-5.58