Over the past few weeks the conversation about sales tax has been pretty consistent and fairly intense. That is probably as it should be given the overall importance of revenue generation across the state right now. What have I done so far? I think the best thing to date may be the discussion surrounding the rolling twelve month series used by the city. Rather than accuracy it is more about stability. Eleven of twelve months in the series are the same from one month to the next so of course the series is stable. The flaws of this approach can be seen when you look at the recent decline. A good month is totally outweighed by the totality of the previous eleven. It also begs a statistical question: should all these months be given equal weight while in the series and then just disappear? That seems highly suspect.
Recent posts clearly place me in the camp of “critic” for the sales tax data from Grand Forks. Criticism can be important because it encourages us to make things better, to improve upon the inadequate. With that in mind I offer up some alternatives that might be better than the current system. If we need to remove some of the “ups-and-downs” of the data, for whatever reason, let’s try to keep the some of the features of the data that keep us in the realm of informing policy. This first graph is for a long period of time and may be a bit difficult to see.
Last week I argued (here) that the city’s use of the rolling twelve month total was not really about accuracy as much as stability. Essentially the two concepts are conflated in the presentation. I still fail to see the virtues of knowing the total sales over the last twelve months, and how it better informs policy decisions. I present the following graphs to demonstrate my points about stability. Here is the monthly collection amount (recall there is approximately a two month lag between sales tax collections and the reported amount).
The March 2018 release came out and did not provide a ton of good news. The new data represents events of January 2018 and therefore pushes us through the entire holiday season. The March 2018 data was down 4.79% from the March 2017. The first quarter of 2018 declined 6.02% from the first quarter of 2017. The city likes to report a rolling 12 month total. For those that do not know, this means they look at the total for the last twelve months and as a new month is added they drop the oldest month. The city suggests this is more accurate, though I am not clear what the term accuracy implies here. The rolling 12-month total generally crosses multiple fiscal years so it is not really reflective of a specific budget year which would be something like calendar year accumulations. The other issue is this measure is down 19 of the last 20 months.
Grand Forks released retail sales tax collections which are for the month of December 2017. There are various different ways to look at the number. It is a .31% increase over December of 2016. An increase is an increase I suppose, though it should be cause for concern if the general optimism permeating the economy surrounding the tax cut happened to miss Grand Forks. The January and February releases for this year, which represent sales tax collected in November and December of 2017, are around 6.5% less than this time last year. It is also the case that 17 of the last 38 months have been lower than year ago values for sales tax collections.