Disparities between Metro’s Metroscope Model and the Demographers’ Forecasts Richard Lycan Institute on Aging, Portland State University Oregon Academy of Science, February, 2016

Population forecasts do matter Think of Wapato jail Lake Oswego School District overbuilds in the 1970’s Paper will provide examples County coordinated forecasts Multnomah Aging and Disability Services Tualatin Hills Park and Recreation District

Population forecasting for Metro Region Oregon land use planning and population forecasts The Office of Economic Analysis Forecasts The PSU Population Research Center assumes responsibility for county coordinated forecasts. Metro’s planning area is excluded – Metroscope Referred to as the demog- rapher’s forecasts Compare

Metro’s Metroscope model Belongs to a class of metropolitan transportation models, e.g. Empiric Provides support for transportation planning Metroscope developed locally – an urban simulation model A tool for exploring policy options Employment > housing > households + geography Detail on households: age, income, kids, size, type & tenure Does not provide population by age Complex

The Demographer’s model The office of Economic Analysis (OEA): a basic cohort- component model Based on projections of rates for births, deaths, and net migration. The PSU Population Research Center (PRC): a cohort- component model as above plus: Considerations of land availability, housing Coordination with local government, especially planners.

Fertility Mortality Net Migration Fertility and Mortality are based both on what is known about national trends and local variations. Net migration is the most difficult for the demographer to estimate. Recent local trends often a major consideration.

Problem: Forecasts by Metro and PRC/OEA differ Metro forecasts higher growth for Multnomah Co., especially Portland than OEA & lower for Washington Co. Metro’s Metroscope does not provide population forecasts by age of persons rather by age of householder. Workings of Metroscope opaque Difficult to understand how the model works other than by varying assumptions and running it The results are not easily available to other researchers let alone the general public

Metroscope age of householder to age of person Necessary in order to have a common basis for comparing Metroscope to demographer’s forecasts. Requirements: Access Metro KHIA data for census tracts. Convert from age of head to age of person. Households by age (0-24,25-44, 45-54, 55-64, 65+) to Persons by age (0-4, 5-9, 10-14, …., 80-84, 85+) Interpolate between 2010 and the Metro 2035 forecast to get intermediate years.

This represents 2.7 households in tract 1.00 in Multnomah Co. with: OS – owner occupied single family K0 – no kids H4 – 4 person HH I7 – the highest income group A5 – householder age 65+ I developed an Excel VBA tool for extracting data from Metroscope and hope others will make use of it, but it is incidental to this paper.

A tabulation of data from the PUMs file from the American Community Survey shows the numbers of persons by five year age group for households by age class. Where the householder was under age 25 there were persons age 20-24, persons age 25-29, etc. Not all persons age reside in households age 25 and under persons this age live in households where the householder was age By 2035 the number of very old persons in the 55 and older age groups will have gravitated toward the upper end of the age group. The graph below shows the ratio of the number by age group forecast by a cohort model and that imputed from the Metroscope age of householder data. This ratio was used to adjust the age data imputed from Metroscope to reflect the age distribution produced by a cohort model.

The last step was to fill in the population forecasts between 2010 and the 2025 Metroscope forecast. There may be no perfect way to do this. I used a modified cohort model with a constant age specific net migration rate to do this. A trial value for net migration for the age group is supplied and the computed population in 2035 is compared with the 2035 forecast. The trial value is increased or decreased until its prediction is the same as that from the Metroscope based numbers. This is repeated for each of the older age cohorts.

The most apparent difference between the Metro and OEA forecasts is the higher forecast for Multnomah County and lower forecast for Washington County by Metro compared to the OEA forecast. I asked Metro’s economist, Dennis Yee, about this and his response was that scarcity of developable land in Washington Co. would limit growth. Presumably it also would be due to a high level of development due to infill, conversion, and densification in Multnomah County. The largest disparities between the two forecasts are for the and 65 and older populations. Metroscope and OEA forecasts by county Population derived from Metroscope about 5% lower. % Growth Multnomah OEA % Metro % Washington OEA % Metro % Age 65+ OEA – % Metro % The differences by county and age grouping between Metro and OEA are significant, beyond errors in the modeling.

Forecasts for Multnomah Aging and Disability Services Metro’s 2025 total for Multnomah Co. is higher as is their forecast for persons age 60+ PRC forecasts a slight loss of population age 85+. The growth rates for the seven planning areas shows essentially no correlation between Metro and PRC. The two forecasts are very different.

Forecast for Tualatin Hills Park and Recreation District In 2010 the population in THPRD was 224,627. PRC forecasts this to grow to 283,147 by 2030 and Metro forecasts slightly less, 261,160. However, Metro forecasts THPRD to have an increasing share of the county’s population and PRC a decreasing share. By age class PRC forecasts higher growth and growth rates for the and 65+ populations. The largest growth by age group for both populations is the 65 and older group. PRC forecasts considerably more numeric and percentage growth for this group. This is an area of concern to THPRD as it may impact the types of services needed and pricing for seniors.

Conclusions Not a finished piece of research. Methods need refinement Reasons for differences between Metro and OEA/PRC forecasts need exploration Clients in Portland need population projections for counties and tract size areas. Household forecasts by age of head may not suffice. When the authorities on forecasting provide different forecasts users don’t know how which to follow. Oregon planning law probably does not require Metro to produce population forecasts similar the county coordinated forecasts required for other counties, but it would be a useful service if they did. The differing views about growth rates for Washington and Multnomah counties are concerning. For organizations interested in forecasts for older people the disparity between Metro and OEA/PRC forecasts poses problems.

Richard Lycan Institute on Aging College of Urban and Public Affairs Portland State University, Portland, Oregon

Who should you believe? Arguments regarding Metroscope The model is responsive to land use policies It deals with the complex reality of employment, land, and housing The forecast may be self fulfilling Has potential for small area forecasts The model is complex, opaque, and unique It’s performance in predicting 2010 Census values not good Arguments regarding the demographers’ models Simpler and easier to understand Many studies on the accuracy of variations of the cohort model Demographers are continually revising their models Cohort models tend to be based on recent trends Deciding on net migration rates highly subjective

Metroscope 2010 forecast compared to the 2010 Census