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Definition
| a study based on data in which no manipulation of factors has been employed |
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| an observational study in which subjects are selected and then their previous conditions or behaviors are determined |
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| an observational study in which subjects are followed to observe future outcomes; because no treatments are deliberately applied, it is not an experiment |
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| an experiment MANIPULATES factor levels to create treatments, RANDOMLY ASSIGNS subjects to these treatment levels, and then COMPARES the responses of the subject groups across treatment levels |
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| to be valid, an experiment must assign experimental units to treatment groups at random |
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| a variable whose levels are manipulated by the experimenter |
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| a variable whose values are compared across different treatments |
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| individuals on whom an experiment is performed, called subjects or participants when human |
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| the specific values that the experimenter chooses for a factor are the levels of a factor |
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| the process, intervention, or other controlled circumstance applied to randomly assigned experimental units; different levels of a single factor or made up of combinations of levels of 2 or more factors |
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| principles of experimental design |
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Definition
| CONTROL, RANDOMIZE, REPLICATE, BLOCK |
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| statistically significant |
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Definition
| when an observed difference is too large for us to believe that it is likely to have occurred naturally |
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| the experiment units assigned to a baseline treatment level, typically either the default or placebo treatment; responses provide a basis for comparison |
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| any individual associated with an experiment who is not aware of how subjects have been allocated to treatment groups |
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single blind: subjects or evaluators are blinded
double blind: subjects and evaluators are blinded |
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| a treatment known to have no effect, administered so that all groups experience the same conditions |
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| the tendency of many human subjects (often 20% or more of experiment subjects) to show a response even when administered a placebo |
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| when groups of experimental units are similar, it is often a good idea to gather them together into blocks; blocking isolates the variability attributable to the differences between the blocks so that we can see the differences cause by the treatments more clearly |
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| in an observational study, subjects who are similar in ways not under study may be matched and then compared with each other on the variables of interest; reduces unwanted variation |
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Definition
| in a completely randomized design, all experimental units have an equal chance of receiving any treatment; in a randomized block design, the randomization occurs only within the blocks |
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Definition
| when the levels of one factor are associated with the levels of another factor in such a way that their effects cannot be separated |
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