Section 5.2 Designing Experiments AP Statistics Section 5.2 Designing Experiments

Objective: To be able to identify and use different experimental design techniques. Experimental Units: objects on which the experiment is done. Subjects: when the experimental units are humans. Treatment: a specific experimental condition that is applied to the units. It is usually a combination of one level from each factor. Factors: explanatory variables in an experiment that the researcher can manipulate.

Levels: the possible values for each factor. Ex Levels: the possible values for each factor. Ex. Create a treatment diagram for a new experiment that has two factors, dosage and frequency. The dosage levels are 100mg and 200 mg while the frequency levels are every 2, 4 or 6 hours. Simple design: Treatment  Observe Response (not reliable) Comparative: Observe Resp.  Treatment Observe Resp.

Placebo: a dummy or sham treatment Placebo: a dummy or sham treatment. Should look/taste/smell/feel just like the real treatment. Placebo Effect: when subjects receiving the placebo actually have positive reaction to it. Control Group: subjects in this group receive the current treatment or the placebo. Must have so we have something to compare the real treatment with.

Three Components of Experimental Design Control: the effort to minimize variability in the way the experimental units are obtained and treated. Uncontrolled studies tend to have higher success rates. Comparison of several treatments is the simplest form of control. Randomization: the use of chance to make an assignment of experimental units to treatments. It is done in such a way that it does not rely on the experimenters judgment. Replication: the use of many units to reduce chance variation. Using many subjects makes the experiment more sensitive to treatment differences.

Statistically Significant: when an observed effect is so large that it would rarely occur by chance alone. Types of Experimental Design: Completely Randomized Design: (CRD) when all the subjects are randomly assigned to the treatments. Basic Diagram:

Randomized Block Design: Begins with dividing the subjects into blocks Randomized Block Design: Begins with dividing the subjects into blocks. (A block is a group of experimental units that are similar in ways that are expected to affect the response to treatments.) After the subjects are blocked, randomization of units to treatments is carried out within each block. WE BLOCK TO REDUCE VARIATION IN THE RESPONSES Basic diagram:

Matched Pairs Design: Type of block design. Compares only 2 treatments. First Type: Pair subjects together that are as similar as possible as many characteristics as possible. Within each pair randomly assign one subject the first treatment and the remaining subject will then receive the second treatment. OR Second Type: Each subject serves as their own block. Every subject will receive both treatments. Randomization is used to eliminate order as a confounding factor. The order of the treatments is randomized for each subject.

Single-blind study: the subject does not know which treatment they are receiving. Double-blind study: neither the subject or the doctor know which treatment is being received or administered. A third party records the results. Lack of realism: one of the most serious and potential weaknesses in an experiment. Sometimes experimental settings cannot be replicated.