Producing Data, Randomization, and Experimental Design, Lecture notes of Experimental Design

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Producing Data, Randomization,

and Experimental Design

Goals

 Identify observational studies versus experiments

 Design experiments to test hypotheses using appropriate randomization

 Use the random number tables to assign subjects correctly to experimental groups

 Define, use, and know the concepts behind all the new vocabulary words

Observational Study vs. Experiment

 Observational study observes and

measures variables of interest.

 Experiment imposes a treatment

in order to observe outcome

New Terminology

 Population Sample

 Voluntary response sample

 Convenience sampling

 Bias

 Simple random sample (SRS)

Other Sampling Designs

 Probability sample

 Individuals chosen with some given probability

 Stratified random sample  Population divided into strata and individuals chosen at random from each strata

 Multistage random sample  Sample chosen in a number of stages

Problems

 Undercoverage: some groups have no chance of being sampled; as in phone polling

 Nonresponse: individuals chosen cannot or will not participate

 Response bias: people may lie about illegal or embarrassing behavior; may respond to the questioner

 Wording of questions may effect the outcome

Example: Television ads

Comparative Experiments

 Compare 2 or more groups

 Use a control group to eliminate confounding and placebo effect

 A randomized comparative experiment uses comparisons between two (or more) groups and randomization of subjects into treatment groups.

Principles of Experimental Design

 Control effects of lurking variables via comparison of several treatments

 Randomization to assign units to treatment

 Replication of experiment on many units to reduce chance variation