Monday, July 27, 2015

Kansas Teacher Salaries: The $7,000 Mistake

Last Friday, Governor Brownback in Kansas held a press conference to cover various topics from abortion to education.  Recent news stories in Kansas had held that teachers were leaving the state  (and profession) in record numbers due to a de-funding of education.  Brownback moved to address this issue with the following chart:

So, if you follow this blog you know I am already annoyed at the chart that's not zero scaled.  But Brownback just annoyed many more people, for far less nerdier reasons.  Turns out, the numbers were wrong, to a scale of about $7,000.  In essence, the administration claimed that teachers made $7,000 more than their Missouri counterparts, when salaries are effectively equal.  The media was immediately all over this, if you want to read more on that here's a summary.  It seems to me this shouldn't be hugely difficult data to validate...

There's another problem here though:  Teachers salaries vary across the country for dozens of legitimate reasons; even if the $7,000 difference was accurate (it wasn't), we shouldn't jump to conclusions before exploring reasons behind variance.


I've looked at teacher pay before in my career, and referenced that before on this blog.  For a quick background, there are several categories of things that impact teacher pay:
  • Attributes specific to teacher (education level, experience)
  • Attributes specific to district (cost of living, ability to pay, working conditions, amenities)
Because the administration is looking at aggregate numbers, the most relevant numbers are the district numbers.  Of those numbers, the most significant by-far is cost of living (Pearson = .77). So, at the very least, any comparison of teacher compensation should look at differences in cost of living.


When addressing teacher pay, generally two accusations made by the teaching community:

  1. Teachers are leaving for Missouri where salaries are higher and conditions are better.
  2. Teachers in Kansas are paid less than those in other states.
For the first point here, I don't know think that State level aggregate data is even the correct analysis.  More interesting would be comparisons of Northeast Kansas to Northwest Missouri salaries, or pairwise comparisons of adjacent border county districts.  

But that's probably not even sufficient for a few reasons.  Teachers are likely leaving not just because of salary differential, but perceived future differentials: They feel things are getting worse, and it will continue that direction (read some media reports in Kansas for context).  That's difficult to measure or model.  Maybe I'll try later this week though.  

But the second question is still out there, and quite a bit easier to answer: adjusted for cost of living, are Kansas teacher salaries similar to national averages?


I used data that's a couple years old, but appears to be the most reliable source on the matter.  In this data, Kansas teachers make in aggregate $47,464, while Missouri teachers make $47,517.  Very close, but the national average is north of $56,000, a number that is pulled up by a few high-population, high cost of living States.  For methodology, I simply regressed the teacher salary data by state against state costs of living.

So what happens if we control for cost of living?  

A couple of points here: 
  • The model is fairly predictive, with cost of living accounting for almost 60% of all aggregate level teacher pay variation.
  • Kansas and Missouri both fall beneath the line.  Kansas has a higher cost of living than Missouri, so it is actually a little worse off.  The by-line here:  Kansas and Missouri both pay teachers between 3.5% and 4% less than national averages, adjusted for cost of living. Here's a summary:

Some nerdyness coming up, so non-nerds can skip...

I had a hypothesis (for various reasons, contact me if you want to know why) that a log-log transformation of this data would fit better.  It didn't really improve results much, and the fit line was essentially the same.  In fact, when I corrected the R-squared from the log-log model (the one stated on chart below is invalid due to the impact on variance of a logarithmic transformation), the R-squares were nearly identical between the two specifications.


Just a couple of quick bullet points:
  • When adjusted for cost of living, Kansas teachers make on average .4% less than Missouri teachers.  
  • Both Kansas and Missouri teachers make at least 3.5% less than the national average.
  • A more in depth study would be required to determine why teachers are leaving the state, including analysis of atmosphere, and perceived future salary risks.  I have a few ideas on how to analyze this, and will try to get to this in the next couple of weeks.