A psychologist has performed the following experiment. For each of 10 sets of identical twins who were born 30 years ago, he recorded their annual incomes according to which twin was born first. The results (in $1,000s) are shown below. Can he infer at 5% significance level that there is a difference in income between the twins?
First born Second born
32 44
36 43
21 28
30 39
49 51
27 25
32 38
42 56
64 44
44 39
What is the appropriate test to perform?