AA testing

1. You're testing advertising emails for a bathing suit company and you test one version of the email 
in February and the other in May.

If this is in the U.S., where summer months start in June, the way the test is conducted is biased because May is too close to summer. 
Results for advertising email in May will be biased.

2. You open a clinic to treat anxiety and find that the people who visit show a higher rate of anxiety than the general population.

The clinic is there to treat anxiety, therefore, only people with anxiety will come to the clinic. 


3.You launch a new ad billboard based campaign and see an increase in website visits in the first week.

One week is too short of a time. We'd want to see a lasting effect from the billboard. It'd be ideal to measure at a later time. 


4.You launch a loyalty program but see no change in visits in the first week.

The changes will not occur immediately. A loyalty program suggest that it requires a customer to be a participant for a while,
hence the word "loyalty".