The population of big cities may depend on millennials: will they flock to urban locations or leave for the suburbs? New data suggests slightly more of them are headed out of cities:

Cities with more than a half million people collectively lost almost 27,000 residents age 25 to 39 in 2018, according to a Wall Street Journal analysis of the figures. It was the fourth consecutive year that big cities saw this population of young adults shrink. New York, Chicago, Houston, San Francisco, Las Vegas, Washington and Portland, Ore., were among those that lost large numbers of residents in this age group…

The 2018 drop was driven by a fall in the number of urban residents between 35 and 39 years old. While the number of adults younger than that rose in big cities, those gains have tapered off in recent years.

Separate Census figures show the majority of people in these age groups who leave cities move to nearby suburbs or the suburbs of other metro areas.

City officials say that high housing costs and poor schools are main reasons that people are leaving. Although millennials—the cohort born between 1981 and 1996—are marrying and having children at lower rates than previous generations, those who do are following in their footsteps and often settling down in suburbs.

An interesting update: millennials as a whole are leaving cities but younger millennials are still going to cities while the oldest ones are leaving. Does this mean that the argument that young urbanites will still leave for the suburbs when they form families and have kids?

Maybe, maybe not. It would be helpful to know more:

1. How does the older millennial move out of cities compare to previous generations? Are they leaving cities at similar rates or not?

2. Is there significant variation (a) within cities over 500,000 people and (b) within smaller big cities (of which there are many)? The first point could get at some patterns related to housing prices. The second could get at a broader picture of urban patterns by not focusing just on the largest cities.

3. The true numbers to know (which are unknowable right now): what will the numbers be in the future? The chart above suggests some shifts even in the last decade. Which pattern will win out over time (or will the numbers be relatively flat, which they are for a number of the years discussed above)?