Simon developed two forms of an intelligence test. In the second form, he changed the wording and order of the questions. He administered both forms to the same group of participants two weeks apart. While scoring the tests, Simon realized that the participants' answers to the different forms of the test were dissimilar. In this case, the tests are said to have:

Mankiw attributes – chapter 1 and his 10 principles – differences in living standards within a countryover time and across countries at a moment in time to: a. the presence or absence of inflation and unemployment.b. the allocation of resources between private markets and the public sector.c. those that have dealt successfully with the efficiency v. equality tradeoff and those that haven’t.d. differences in productivity.e. ones that think at the margin and respond to incentives and those that don’t.