1. Experiments
Observational Study – observes individuals and measures variables of interest but does not attempt to influence the responses.
Experiment – deliberately imposes some treatment on individuals in order to observe their response.
Treatment – an experimental condition applied to the units.

2. Experiments
Experimental Units – individuals on which the experiment is done. Subjects – what human experimental units are called.

3. Experiments
Response Variable – measures an outcome of a study. Also referred to as the “y” variable. Explanatory Variable – attempts to explain the observed outcomes. Also referred to as the “x” variable.

4. Experiments
Lurking Variable – a variable that is not among the explanatory or response variables in a study and yet may influence the interpretation of relationships among these variables. Confounding – variables are confounded when their effects on a response variable cannot be distinguished from each other. Confounded variables may be explanatory or lurking. Example p. 270.

5. Experiments
Factors – the explanatory variables in an experiment. Levels (treatments) – different values of each factor. Example p. 290

6. Experiments
Placebo – a dummy pill or treatment that looks and tastes like the treatment but has no active ingredients. Placebo Effect – Response to a dummy treatment. Control Group – the group of patients who receive the placebo. The control group allows us to control the effects of outside variables on the outcome.

7. Experiments