Objective: Use experimental methods to design our own experiments Homework: Read section 6.1 and 6.2 (for vocab and examples) and then complete exercises: 6.19, 6.20, 6.21, 6.26, 6.27, 6.28, 6.33, 6.36

What is wrong with this experiment design? A credit card bank wanted to test the sensitivity of the market to two factors: the annual fee charged for a card and the annual percentage rate charged. The bank selected 100,000 people at random from a mailing list. It sent out offers with a low rate and no fee and offers with a higher rate and a$50 annual fee.

The subjects signed up for the lower rate, no fee card at twice the rate of the other The question the bank wanted to answer was: how much of the change was due to the rate and how much was due to the fee? How could they have designed their experiment better?

Lurking / Confounding? Lurking variables can be thought of as a prior cause of both y and x that makes it appear that x may be causing y ( in observational studies and in regression). A confounding variable is associated in a noncausal way with a factor and effects the response. We can’t tell whether the effect was caused by our factor or by the confounding variable ( in experiments).

What is it? There is found to be a positive association between ice cream sales and number of drownings. This is a clear example of a lurking variable- the season (summer time) has both more ice cream sales and also more drownings.

A recent medical study found that among men who have had a heart attack, those with a higher level of a certain protein in their blood are at greater risk to have a second attack. What can you conclude from this study? Nothing much. Maybe the protein caused the second heart attack, maybe it was just something that occurred in both, or as a result of the heart attack.

Smoking A retrospective study that finds most people with lung cancer were smokers A prospective study which follows a group of smokers and nonsmokers for several years An experiment on 10 year olds…

From Newsweek: Of all the pre-college curricula, the highest level of mathematics one studies in secondary school has the strongest continuing influence on bachelor’s degree completion. Finishing a course beyond Algebra 2 more than doubles the odds that a student who enters post-secondary education will complete a bachelor’s degree. Propose a study design to study that might enable you to draw this conclusion (at least a causal one)

Ethical Concerns Is it okay to use animals for experiments? Does it matter for what purpose? What is “informed consent?” Is it okay to drill placebo holes in patients’ skulls so that they and their doctors won’t know whether or not they received an experimental implantation of nerve cells as a possible treatment for Parkinson’s Disease? (this was actually done).