AP Statistics Unit 3

double blind

when the subjects as well as those evaluating the result of an experiment do not know which subjects are in the treatment or control groups

placebo

a fake treatment often given to the control group to help prevent the placebo effect (subjects improving by the power of suggestion)

blocking

subjects or experimental units are grouped together homogeneously because of some charcteristic they have in common that is believed might effect the experiment

confounding

when the results of an experiment can be determined because a variable has not be accounted for and has interferred with your results

convenience sampling

a poor way to collect a sample - do what is convenient for the surveyor, data is usually very biased

prospective study

a study where we collect data as it happens

retrospective study

a study where we collect data from events that have happened in the past