<p>@fallenchemist </p>
<p>Please read my post more clearly. </p>
<p>I said: “It is obvious that the correlation is caused by:
The obvious relationship between high grades and hard-working habits/intelligence. Hard-working habits/intelligence tend to remain in university which leads to higher paying jobs.”</p>
<p>You said: "How can you say there is no correlation between high school GPA and income? "</p>
<p>When I said “It is obvious that the correlation is caused by:” it means I know that there is a correlation, just not for certain reasons. </p>