Monday, May 19, 2014

Post Soylent (city of) Pittsburgh

A number folks out there (I'm projecting of course) are waiting for the latest (2013) population estimate for the City of Pittsburgh. That will come with the release of subcounty population estimates from the Census gnomes on Thursday.

The city's population has been moving target of late. Go back two years and the estimate of the city's population in 2011 showed a jump of a whopping 1,780 people over 2010, an increase that marked the first population increase for the city of Pittsburgh in at least 60 years if not longer.  You may note my caution with that data in the only coverage that year. There was a reason, actually several reasons, I doubted that estimate would hold up into the future.

Skip ahead a year and the estimate for 2012 showed another increase, but a paltry 152 folks, but the big jump the year before was mostly revised away. That +1,780 jump between 2010 and 2011 was revised downward to a jump of +542. So still an increase, but far from what was reported a year earlier and still a number with both data and methodological questions that make it hard to conclude there really was an increase. Still, error or not, any increase is better than the decrease that has been the norm since forever for the city. The last decade the city showed population gains? Between 1930 and 1940, but that has been estimated to be the result of a few marginal annexations to the city proper, not any population growth per se.

So we wait for 2013's population estimate and any possible revisions of previous data.  Will population in the city decrease or increase, and if so by more or less than the net gain of 152 in the most recent year? Here is the problem. Population change comes from only two trends: natural population change (births minus deaths) and net migration. Lets just look at the first trend there.. births.  Here is the trend in annual births to city of Pittsburgh residents from 1990 to the most recent data in 2012. 

What jumps out is that for the latest (2012) data on number of births among city of Pittsburgh residents is the lowest it has ever been. A bump up 6 years prior does not appear to have been the start of any trend. That may be a story unto itself, but hold that thought. So even though the population estimates showed an increase it wasn't because of any trend up in local births, in fact the drop in births between 2011 and 2012 was pretty steep percentage wise.

How many fewer kids are there in the city? The number of births in 2012 was 3,340. In 1960 the city's population of those less than one year of age was 12,011, suggesting the number of births the year prior.

But natural population change is births minus deaths.  Here is the same birth data matched with annual deaths in the city of Pittsburgh.  So the number of local deaths is itself dropping even faster than the number of births.  The local funeral home biz must not be what it once was even just a few years ago. Also probably a story in that as well. But births have exceeded deaths in the city for 6 years at least.

The net difference between births and deaths for the city was positive between 2011 and 2012 by 400.  So if you believe the +152 population gain,, net migration would still have to be negative for the city proper.  But the 152 number is way more precise than you want to hang your hat on. Still, there is broad conclusion that if the city's population has stabilized at the very least, the main reason is that we have reached a point of demographic exhaustion... basically the rate of city residents dying off has slowed. So even with the historically low number of births, the continuing drop in the number of deaths has pushed natural population gain positive for the city proper (though it remains negative for the region) and is enough to offset even minor migration losses, not that we really have hard data for net migration at the municipal level. 


Anonymous BrianTH said...

Hmm, yet another reason to believe there could have been a City population trend inflection point in the mid-2000s, which could not be detected if you are only working with decennial census data.

Speaking of which, did we ever figure out what was going on with the City's apparently low count of residential building permits in recent years? Last we left it, the reported numbers did not seem to be capturing a lot of known residential projects (mostly, but not exclusively, conversions).

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