I'm trying to answer a very simple question: by how much has the under 18 population in San Francisco changed since the pandemic.
The 2020 census redistricting data gives the population of San Francisco at 873,965, of which 760,738 were 18 years and over. That implies the U18 population was 113,227.
Table P12 in the Demographic and Housing Characteristics gives the same total and breaks it down by age and sex. So far, so good.
My understanding is that the Population Estimates Program is the place to go for intercensal estimates of the population count.
I downloaded the latest vintage age/sex breakdown by county. Here's the San Francisco data for select age buckets.
The total population figure in the base year is very close to the census figure, which is what I'd expect. Notice that the 0-17 population in the base year is estimated to 118,989 whereas the census gave a figure of 113,227. That's a 5% difference which is way beyond any margin of error.
Meanwhile, the ACS 1-year estimates are consistent with the population estimates:
Questions:
1) Why is the base year U18 population estimate so different from the census figure (118,989 vs 113,227)? Isn't the former supposed to be based on the latter?
2) Which number should I use? I want to use the 2020 census figure because then I've got a consistent series going back decades but comparing the census figure with the 2023 estimates implies that the U18 population fell by only 3,000 which is not credible for two reasons.
3) Even if we forget about the census completely, I struggle to believe the age breakdown of the population change implied by the ACS surveys and population estimates. Are we really to believe that a pandemic that killed mainly old people and led to 70,000 people leaving the city somehow caused the population 65 and over to increase by 8,500 and the population aged 75-79 to increase by nearly 25% in three years? If true, I would have expected this influx of retirees to be covered in the local media.
hi Paul--
I'll try to answer your questions.Yes, there are multiple annual population estimates datasets.
I will list four products. But one of these is not yet available -- 'for reasons'. And so, Postcensal Estimates from Census PEP is probably a best option.
Four products:
1. Postcensal Estimates from Census PEP. These are built up, since the previous decennial census, with annual demographic progression. i.e. 2010 is the 'base year' for 2011-19 estimates; 2020 is the base year for 2021-29. Because of that there can be a time-series break, or 'cliff', at the decennial year. So, interpret cautiously!I am simplifying in this description -- there's far more could be said. See https://www.census.gov/programs-surveys/popest/guidance.html
2. Intercensal Estimates from Census PEP. This is (or will be) a subsequent product in which Census PEP tries to reconcile and smooth out the annual time-series. Unfortunately, Census PEP has not released this product yet. And... does anyone know the release date? (Census website says "Fall 2024"...)
3. Population data in ACS. This should be only minimally/minorly different from the Postcensal Estimates already mentioned, because Postcensal Estimates provide ACS's population totals. But, a difference from product 1 above, Census Bureau does *not* revise the ACS stats once they're published. Postcensal Estimates from PEP can be revised, and are revised as data sources, improve and trends become clearer.Again, I am simplifying in this description.
4. Annual Population Estimates (typically postcensal) from your State Demographer or State Population Analyst. Many states want to be more in control of the population data they use, so they have their own population estimates products -- 'for reasons'. The bad news is: it's only half the states that have the state products; and they're mostly concerned with total population, households and housing totals. Very few (there are some) are parsing the estimates into age groups or other demographic categories.
You asked some questions: Which of these to use? The answer is: it depends. If your inquiry includes change over time -- and extending across the decennial census timepoint, then I feel like you want the product with the least amount of time-series disruption. You'll need to figure that out for your case.
You also asked if the speed of senior citizens increase is 'believable'? In my view, yes -- what's not to believe? There’s a substantial aging wave underway, mostly during 2010 thru 2030. In the metro where I am, we project ~ 10% increases annually. This is not due to migration here – this is due to Baby Boomers (and subsequent generations) aging into the 65+ and 75+ brackets. It's due the massive size of the Baby Boom generation (and subsequent generations), and the fact that Baby Boom is the first cohort to enjoy the long life expectancies that came out of 20th century public health and medical advances.
That's a long answer -- hope it helps.
--todd graham principal demographer, Metropolitan Council of the Twin Cities (METC)