Observational Study: Studies where data are collected only by monitoring what occurs
Experimental Study: Studies where yours sample is introduced to a new variable to be tested
Control Group: The portion of the sample that is unaffected by the tested variable
Treatment Group: The portion of the sample that is affected by the tested variable
Completely randomized experiment: Subjects are randomly assigned to each group in the experiment
Blocked experiment: Subjects grouped based on the identified variable
Randomize subjects within each group as control or treatment
Matched pairs experiment: Pairs of people are matched on as many variables as possible, so that the comparison happens between very similar cases. One is made a control, the other treatment.