Graphs have been around for a long time. They show, for example, the relationship between the unemployment rate and level of education. I will send you the graph. Four levels of education are very clearly distinguished: people who have a university degree, people who have another post-secondary degree, those who have a high school diploma and those who do not have a high school diploma. The four lines are parallel. As the level of education goes up, the unemployment rate goes down. Moreover, when the economy fluctuates, we see that people with a higher level of education are less affected by economic cycles. Their unemployment rate is more constant, whereas those who have a lower level of education, especially people who have not completed high school, have a much higher unemployment rate which fluctuates much more with the economic cycles.
On June 13th, 2006. See this statement in context.