| A | B |
|---|
| Observational study | based on data in which no manipulation of factors has been employed |
| Retrospective study | observation of previous conditions |
| Prospective study | focus on estimating diferences among groups that might appear as teh groups are folowed during the course of the study |
| Experiment | manipulates factor levels to created treatments, randomly assigns subjects to these treatment levels, and then compares the responses of the subject groups across treatment levels |
| Factor | a variable whose levels are controlled by the experimenter. |
| Respnse | A variable whose values are compared across different treatments. In a randomized experiment, large response differences can be attributed to the effect of differences in treatment level. |
| Experimental units | Individuals on whom an experiment is performed. Usually called subjects or participants when the are human. |
| Level | The specific values that the experimenter chooses for a factor. |
| Treatment | The process, intervention, or other controlled circumstance applied to randomly assigned experimental units. Treatments are the different levels of a single factor or are made p of combinations of levels of two or more factors. |
| Principle of experimental design | Control, Randomization, Replication, Block |
| Statistically significant | observed difference is to large to have occurred naturally |
| Control group | baseline treatment level - placebo - provides basis for comparison |
| Blinding | any individual associated with an experiment who is not aware of how subjects have been allocated to treatment groups is said to be blind. |
| Single blind | those who could influence results are blinded |
| Double blind | Those who evaluate results are blinded as well as those who could inluence results |
| Placebo | A treatment know to have no effect |
| Placebo Effect | tendency of many human subjects to show response even when administered a placebo |
| Block | Grouped experimental units due to similarity - helps us see differences attributable to the treatment more clearly |
| Matching | In observational study, subjects who are similar in ways not under studey may be matched and then compred with each other on the variables of interest. Like blocking, it reduces unwanted variation |
| Randomized Block Design | Randomization occurs only within blocks |
| Completely randomized design | all exp. units have an equal chance of receiving any treatment |
| Confounding | When the levels of multiple factors are associated with each other so that their effects cannot be separated. |
