For each experiment that follows, identify the independent variable and its levels. Identify the dependent variable. State the null hypothesis in words.
a. A psychologist compared the annual income of people with high Satisfaction With Life Scale scores to the income of those with low SWLS scores.
b. A sociologist compared the numbers of years served in prison by those convicted of robbery and those convicted of embezzlement.
c. A physical therapist measured flexibility after 1 week of treatment and again after 6 weeks of treatment for 40 patients.