Southern California’s housing construction runs one-quarter slower than required to keep up with population growth, by one accounting.

I filled my trusty spreadsheet with apartment tracker RentHop’s compilation of population growth and housing permits from 2010 to 2016. It tells me that builders in the four-county region filed permits for 205,959 residential units in the period while the population grew by 770,829.

All that construction translates to new Southern California housing that holds, on average, 3.7 extra people in each permitted unit. But please note the typical Southern California household is home to three people. So, we’re losing ground!

I estimate the region’s construction since 2010 is 51,000 homes short, assuming a 3-to-1 ratio of people to permits is what the market needs just to stay at in the ballpark of status quo. That’s means we should have built 25 percent more homes! (FYI: In 30 large metros tracked by RentHop, the median people-to-permit ratio was 3.1 in 2010-2016.)

So, can you see why Southern Californians double up as rents and home prices soar?

Here’s what RentHop’s population-to-permit stats say about the individual counties and meeting a 3-to-1 ratio of people to permits:

Orange County: Doing the best, as it’s 55,575 units permits vs. 154,885 in population growth adds up to a 2.8 people-per-permit ratio. Assuming the 3-to-1 target, it’s actually 4,000 ahead of pace.

Los Angeles County: Ranks next with 97,549 units and 319,310 in population growth for a 3.3 people-per-permit ratio. That’s roughly 9,000 short.

San Bernardino County: Third, with 19,680 units vs. 98,534 more people, or five people per permit. The county missed my target by about 13,000.

Riverside County: Worst, with 33,155 units permitted and 198,100 more residents. The six people-per-permit ratio is 33,000 less than the target and also was third worst among 30 large markets tracked.