The question eats away at city leaders: Can Philadelphia retain the millennials who’ve come to the city to work and play the last several years?

Michael Nutter’s administration created an advisory board to intended to keep young people here and get them to work in local government. Campus Philly has worked to reduce the number of graduates from Philadelphia colleges leaving the city for years.   

Recently, some good news and bad news arrived with regards to this question. First, the bad: Young people are moving away from Philly. Lots of them. The good news is it could be a lot worse. A recent report shows how people in Philly ages 18-to-34 are moving away at a rate lower than might be expected, compared to other big cities across the United States like New York, Washington DC and San Francisco.

The study comes from the real estate website Trulia. It looked at 10 of the most expensive cities in the United States and their share of millennials, the share of people who move out of the city who are millennials and the move-away rate relative to expectation for millennials.

Seven of these cities are like Philadelphia in that they’re among the United States’ 10 largest, so it’s worth comparing them. Trulia didn’t publish its data on Philadelphia, but shared it with Billy Penn. Here’s how it looks for migration out of Philly and the other cities with regards to age groups:

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The middle number means young people represent about half of all people who have moved away from Philadelphia in a given year between 2009 and 2014. For the other cities highlighted by Trulia, millennials represented between 47 percent and 55 percent of the share of move-outs — about the same as Philadelphia. All things equal, these numbers should be much lower. Millennials make up between about 20-to-30 percent of the overall population in these cities. As Trulia puts it, if 25 percent of a population has brown eyes you’d expect the share of brown-eyed people who move away from a city to represent 25 percent of all movers.  

The 18-to-34 age group will always be higher than other groups because young people are always the most mobile age group, moving around because of college, career or family reasons. Given these variables, the move-away rate relative to expectation was high.

Philadelphia’s move-away rate relative to expectation was 69.8 percent. Los Angeles, Washington DC, New York, San Francisco, San Diego and Chicago all have move-away rates relative to expectation of at least 91 percent.

How does that look in real world terms? How might Philadelphia be different if its move-away rate relative to expectation were 91 percent?

Between 2014 and 2015, Philadelphia had a net loss of domestic residents of about 10,000 people. Based on migration rates from recent years, it’s likely somewhere around 60,000 people moved out of the city to another American city and 50,000 moved in from another American city. According to Trulia, 53 percent of all movers out of Philadelphia have been millennials, so we’ll say 30,000 of those 60,000 movers were between the ages of 18-to-34. In a perfect world, where the brown eyes theory comes into play, only 31 percent of those movers — or about 20,000 people — would have been in that age group. If Philadelphia were like San Francisco and its move-away rate relative to expectation were 91 percent, the number of young people moving out would have been about 38,000. That’s a difference of 8,000 people a year.

It’s possible Philadelphia’s move-away rate relative to expectation is lower than those other cities because it has fewer 18-year-olds moving off to college than, say, New York. It might have little to do with more people in their low 30s choosing not to flee to the suburbs.

But Trulia’s report suggests young people are having a tough time staying in cities like New York and San Francisco because of the sky-high real estate prices. Philly’s comparatively low rents and home prices might be allowing young people to stick around for longer.

And for Philadelphia, a city trying to undo decades of decline and keep its buzz going, positive signs are always welcome.

Mark Dent is a reporter/curator at BillyPenn. He previously worked for the Pittsburgh Post-Gazette, where he covered the Jerry Sandusky scandal, Penn State football and the Penn State administration. His...