AP Stats - Chapter 12 - Experiments and Observational Studies

What have we learned?
We can recognize sample surveys, observational studies, and randomized comparative experiments.
These methods collect data in different ways and lead us to different conclusions.
We can identify retrospective and prospective observational studies and understand the advantages and disadvantages of each.
Only well-designed experiments can allow us to reach cause-and-effect conclusions.
We manipulate levels of treatments to see if the factor we have identified produces changes in our response variable.

What have we learned? (cont.)
We know the principles of experimental design:
Identify and control as many other sources of variability as possible so we can be sure that the variation in the response variable can be attributed to our factor.
Try to equalize the many possible sources of variability that cannot be identified by randomly assigning experimental units to treatments.
Replicate the experiment on as many subjects as possible.
Control the sources of variability we can, and consider blocking to reduce variability from sources we recognize but cannot control.

What have we learned? (cont.)
We’ve learned the value of having a control group and of using blinding and placebo controls.
We can recognize problems posed by confounding variables in experiments and lurking variables in observational studies.