what is the two-tier test?

Answer 1

You leave a lot to the imagination. You have not provided any details in you question, but normally two tier testing involves the following.

It involves two seperate and not necessarily related items. A simple example would be Identify the number of unmaried males who smoke.

You could start by finding either unmarried males, or a total number of people who smoke (male/female/married/single). Lets start with unmarried males. That way you cut out all married people and all females so only about 1/4 of the total population are elegible to have the second question asked. How many of the first answer smoke?