UrbanSim Household Forecasts February Progress

Where we are Run 37 is our best run to date. It is the result of both a model of what’s important to household location choices, plus a set of correction factors based on how well the model predicted 2015 when starting from the 2010 base year. The correction factors use the place types the committee developed to add or subtract growth to different types of areas in the region. Run 36 shows the forecast when we rely on the household choice model alone. It’s the variables in the household location choice model, though, that allow us to create scenarios and run policy tests. So, much work is being put into getting a good forecast without needing to employ the correction factors as much.

Two uncalibrated runs Run 36 Run 37

February progress We did some tests and found that part of the problem resided in a different model within UrbanSim, the housing unit development model. This model determines where new housing units are built. Once built, they are initially vacant, but become available for households to move into. This model was not building enough units in Johnson County for households to occupy We added a dummy variable for Johnson County into the housing unit model, which allows it to capture than Johnson County is somehow different, without attributing that difference to a specific variable. This is consistent with some Committee members’ stated belief that jurisdictions matter, not just socioeconomic variables. Run 39 shows an improvement over run 36.

Two uncalibrated runs Run 36 Run 39

Two uncalibrated runs Run 36 Run 39

Run 39 Run 37 Run 39

In March… We believe that by focusing first on the housing unit model, then the household model, we have identified the path forward to more rapid improvements in forecasting performance. After making some additional modifications, we we will send out a population and household forecast for you to begin reviewing by the end of March.