1. Section 10.3 Making Sense of Statistical Significance
AP Statistics

2. Choosing a level of significance (alpha level)
How plausible is H0?
Depending on H0 plausibility, you may choose a smaller alpha.
If H0 is very plausible, you will need to have collect “more” evidence to reject it.
Example: “You can eat as much as you want and lose weight, as long as you avoid grain products.”

3. What are the consequences of rejecting H0?
If rejecting H0 would
costs lots of money
possibly cost lives
costs jobs
then alpha is usually very small
Example: Global Warming

4. Fishing for significance
Let’s say were trying to find a connection between eating habits and intelligence.
Choose 40 foods, and assign people to increase the amount of the foods they eat, and see if there are any foods that make people smarter.
Of the 40 foods, we find that peeps and green beans make you smarter with alpha=.05. Is this a problem?

5. Fishing for Significance
Yes, this is a problem.
When using alpha=.05 we would expect that by pure chance variation we get significant results once every 20 times.
With 40 foods being tested, about 2 of the foods would have significant results by pure chance.

6. Assignment
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