A reader asks whether the plunge in college enrollment reported this week in census data was fueled by economic trends — as we suggested in an article Tuesday — or demographics.

It’s a good question. We probably should have noted that college enrollment is hugely influenced by the size of the population that recently graduated from high school.

For example, college enrollment obviously rose when the famous baby boomers, born after World War II, started to turn 18 years old. So, the number of 18- to 24-year-olds nationwide obviously has implications for college recruiters.

But the new census data had an interesting wrinkle related to what are sometimes known as “nontraditional” college students, the crowd who are 25 and older.

As we noted Tuesday, there were 16.17 million undergraduates enrolled last October, down from 16.63 million the previous year. The decline of more than 450,000 students was the largest since 1999.

Dig into the data, and you’ll find that number of undergraduates 24 or younger shrank by about 122,000 students from 2011 to 2012. The 25-and-older cohort shrank by about 332,000.

That means the older students accounted for nearly three-fourths of the shrinkage — even though older students only make up about a quarter of the undergraduate population.

Why is this important? Because older students are plugged into the workforce much more than younger students. So, if the economy is stabilizing after the 2008 financial crisis, making the job market more attractive than it was a few years ago, then our inference is that there will be a significant effect on the college-going decisions of the 25-and-older crowd.

But, yes, demographics play a role, too.

Check out the data on Table A-7 of this Web page.