Planning and Conducting ExperimentsEmily Bennett 1st Period

CHARACTERISTICS Well Designed and Well Conducted Experiments

Characteristics…

• Random: The study must be randomized to prevent bias.• Replication: When a study has a large sample or is

performed multiple times it gives more accurate results.• Control: A group that the study can be compared to. This

prevents variability and lurking variables.

MORE INFO ON EXPERIMENTSTreatments, Random Assignments, and Experimental Units

More Info…..

• Treatments: Specific condition being applied to the experimental unit or subject.

• Random Assignments: Used to assign subjects to a certain treatment or to a certain grouping for the treatment.

• Experimental Units: The person, animal or object being experimented on.

SOURCES OF BIAS AND CONFOUNDINGPlacebo, Blinding, etc.

Bias and Confounding…

• Sources of Bias: • Wording of the question being posed. • Characteristics of the interviewer• Response of the subject or subjects• Convenience

Bias and Confounding…

• Confounding: When the affects of two variables cannot be separated.

• Ways to Avoid Bias: • Blinding: When the subject doesn’t know the treatment they will

receive.• Double Blinding: When both the subject and the

experimenter/administrator don’t know the treatment being given/recieved.

• Placebo: Occurs when the subject thinks and believes that they will be affected by the treatment, so they are.

COMPLETELY RANDOMIZED DESIGNThe Simplest Experimental Design

Completely Randomized Design…

• Subjects are randomly assigned to treatments.• There are usually only 2 treatments• Often times a placebo is given to one subject and the

experiment is given to another subject.• Relies on randomization to eliminate variability

RANDOMIZED BLOCK DESIGNIncluding Matched Pairs

Block Design

• Steps of the Randomized Block Design:• Divide subjects or participants into blocks based on certain

characteristics.• RANDOMLY assign experimental subjects or units to

treatments within each block. • Compare results WITHIN each block.

• Matched Pairs: A block design only when there are two units.

Types of Experiments

• SRS—Simple Random Sample• When all of the population has the same chance of being the

sample that is selected.• Clustering• Dividing sample into groups that share similar

characteristics, then randomly choose some clusters to be tested/experimented on.

Works Cited

• My written notes, tests, reviews and note sheets.• www.ma.utexas.edu/users/mks/statmistakes/SRS.html• http://m.wisegeek.org/what-is-cluster-sampling.htm

• http://stattrek.com/statistics/dictionary.aspx?definition=completely_randomized_design