“Is there sufficient evidence that middle-class heads of households who work for someone else (OCCAT1: 1 = Someone else, 2 = Self employed/partnership) have higher incomes that heads of households who are self-employed (INCOME)?”

a. What is the required condition for a t-test of the difference between two means? Is it satisfied? If not, what technique should be used?

b. Use the appropriate method to answer the question about employment and income.