Once again, the FYI Guy at the Times leaves us scratching our pointy little Indexer head, and waking in the night muttering “Margin of Error, Margin of Error!”
A teachable moment! And a chance to focus on a delightful part of our state.
In a September 18 column, the FYI Guy reviewed migration data from the Census Bureau’s American Community Survey (ACS). Among the peculiar data points, the story reported that 803 people moved from Cowlitz County to King County in 2018, and only 54 people moved from King County to Cowlitz County.
This just seemed odd. First, 803 people constitutes nearly one percent of the county’s population. Second, people are moving into King County from smaller and more rural counties at a very low rate. So what’s going on?
The easiest place to start is with the margin of error (MOE) inherent in survey sampling. The ACS asks a long list of questions to about 1 percent of the nation’s population each year—about 1,000 people in Cowlitz County. And according to the ACS, no more than 3.7 percent of Cowlitz County residents moved from another county in Washington in 2018.
Correctly identifying 3.7 percent within 1 percent is looking for a needle in the demographic haystack. And as it turns out, the MOE (not the bartender in the Simpsons) for the data cited by FYI is really big.
But the good news is that there is a much better answer to this question. The Internal Revenue Service collects data on address changes on tax returns, and publishes that data in county pairs, giving us the best migration data to be had. The most recent data covers tax returns filed in 2018 for the 2017 tax year. Figure 1 shows the ranges of the ACS data and the actual IRS data.
So why are the ACS estimates so far from the IRS data? The MOE comes with a caveat. There is a 90 percent chance that the real number is somewhere within the interval defined by the MOE. So there is a 10 percent chance that the real number is outside the interval, and it looks like we hit that 10 percent.
A net inflow into Cowlitz County makes sense. Cowlitz County is one of the state’s legacy forest products areas, and has had its share of struggles in recent decades. But it seems to be doing quite well now. Pre-pandemic unemployment was around 5 percent and employment recovery is proceeding well. The county has enjoyed a strong net inflow of people for a number of years, mostly from southwest Washington and the Portland area. Per capita personal income in Cowlitz County has increased an average of 3.4 percent per year since 2010 and home prices are up 20 percent in the past year.
Figure 2 show the IRS figures for top origins of in-migrants and top destinations of out-migrants for Cowlitz County in 2018.
If you are heading to Portland and can’t do the full Wahkiakum, do stop in Longview and look for the squirrel bridges built and maintained by a local group of civic leaders in red-striped blazers. Pretty sure these guy are not moving to King County.
Very nice!