They didn&#x27;t take a study specifically to find out how many people have a college degree, they likely did a study of studies tracking all the studies (of which there are many) that <i>somewhere</i> ask people their age and education level.<p>Mapping all that together gives you this result.<p>Most studies that aren&#x27;t about age-specific tasks or topics will gradiate on 17-20 &#x2F; 20-24.<p>Remember all those studies that look at teenage pregnancy rates in the 17-20 age? Heh, studies of studies.