 | Term | Definition |
| |
experiment |
an experiment 'manipulates' factor levels to create treatments, 'randomly' assigns subjects to these treatments levels, and then 'compares' the responses of the subject groups across treatment levels |
| |
random assignment |
to be valid, an experiment must assign experimental units to treatment groups at random. this is called random assignment |
| |
factor |
a variable whose levels are controlled by the experimenter; experiments attempt to discover the effects that differences in factor levels may have on the responses of the experimental units |
| |
response |
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 unit |
individuals on whom an experiment is performed; usually called 'subjects' or 'participants' when human |
| |
level |
specific values that the expeerimenter chooses for a factor are called the levels of the factor |
| |
treatment |
the process, intervention or other controlled circumstance applied to randomly assigned experimentals units. treatments are the differnt levels of a single factor or are made up of combinations of levels of two ore more factors |
| |
principles of expermental design |
control, randomize, replicate, and block |
| |
control |
control aspects of the experiment that we know may have an effect on the response, but that are not the factors being studied |
| |
randomize |
randomize subjects to treatments to even out the effects that we cannot control |
| |
replicate |
replicate over as many subjects as possible. results for a single subject are just anecdotes; if the subjects are not a representative sample from the population of intereest, replicate the entire study with a different group of subjects, preferably from a different part of the population |
| |
block |
block to reduce the effects of identifiable attributes of the subjects that cannot be controlled |
| |
statistically significant |
when an observed difference is too large for us to believe that it is likely to have occurred naturally, we consider the difference to be statistically significant |
| |
control group |
the experimental units assigned to a baseline treatment level, typically either the default treatment, which is well understood or null, placebo treatment. their responses provide the 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 |
when every individual in either the 'influence' or 'evaluation' class is blinded its single | those who could 'influence the results' ; ex. the subjects, treatment administrators, or technicians |
| |
double blind |
when everyone in the 'influence' and 'evaluation' classes is blinded its double | those who 'evaluate the results'; ex. judges, treating physicians, etc |
| |
placebo |
a treatment known to have no effect. |
| |
placebo effect |
the tendency of many human subjects [ often 20% ] to show a response even when administred a placebo |
| |
matching |
matching, like blocking reducdes unwanted variation; in a retrospective or prospective study, subjects who are similar in ways not under study may be matched and then compared with each other on the variables of interest |
| |
designs |
randomized block design and completely randomized design |
| |
confounding |
confusing or surprising results; when the levels of one factor are associated with the levels of another factor so their effects cannot be separated, we say that these two factors are confounded |
| |
randomized block design |
the randomization occurs only within blocks |
| |
completly randomized design |
all experimental units have an equal chance of receiving any treatment |
Share on Facebook
Share on MySpace