Between 1990 and 2000 there are large increases in the population of people with disabilities as related to transportation. The questions asked on the long form changed substantially and the data is presented differently. In 1990, the data was presented as people who have either mobility or self-care disabilities (I suppose you chose one or both). In 2000, I believe the question was formatted to ask if people had disabilities that affected their ability to travel outside the home. The data is presented by type of disability including Sensory, Physical, Mental, Self-Care, Go-Outside-Home, and Employment disabilities.

I am wondering if anyone knows how much of the increase in the number of people reporting "Go-Outside-Home Disabilities" over the 1990 "Mobility Limitations" is due to the way in which the questions were asked and how much is due to increases in this population? The elderly have a higher incidence of disabilities so as the elderly population increases one would expect an increase in the numbers of people with "Mobility" or "Go-Outside-Home" disabilities. Also, the incidence of certain kinds of disabilities has been increasing in new-borns.

In the past I have used formulas to calculate transit demand for the general population or for the population of the elderly and disabled. They are calibrated based on the 1990 definitions. When I use the 2000 numbers, there are some definite problems - the formula for Elderly and Disabled trip demand is higher than the Total trip demand. How might I need to adjust these to account for differences in the definitions? Has anyone worked on adjusting or re-calibrating demand formulas based on the new definitions and actual ridership in communities?