Suppose a researcher was interested in studying whether one's level of post-secondary education affects their income soon after graduating. They administer a survey to a sample of 500 recent university graduates. Among other variables, the researcher asks respondents to report their highest diploma or degree obtained and their income in the first full year after their graduation. The variables are coded as follows:

Education level:

1. College diploma
2. Bachelor's degree
3. Master's degree
4. PhD

Income:

1. Low
2. Middle
3. High

The researcher finds a statistically significant relationship between these two variables and proceeds to produce a series of measures of association to understand this relationship more fully. They calculate the following:

Gamma = 0.71

Tau-b = 0.32

Tau-c = 0.31

Somer's d = 0.33

a) Which variable is the independent variable and which variable is the dependent variable? (/1 mark)

b) Which measure(s) should the researcher interpret, and which, if any, should they ignore? Why? (/3 marks)

c) What is the researcher's interpretation? (/1 mark)