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60 I N N O VAT I O N S I N T R AV E L D E M A N D M O D E L I N G , V O L U M E 2 forecast year. The benefits in the forecast year of more regional sizes of the subpopulations age 65+ and less size categories would probably be much greater if ARC than 15. The forecast control categories are sized by could forecast a household size distribution rather than using relationships in the base-year census PUMS data an average household size. between the available values and the needed control cat- egories. In the base year, the controls noticeably improve the accuracy and precision of the corresponding house- Employment hold categories. However, in the back-cast, Version 316 controls provide no apparent improvement in accuracy Employment is controlled as number of workers in a or precision over the uncontrolled Versions 52 and 128, household, in four categories, with TAZ-level control in and, for the presence of children under the age of 18, the base year. In the forecast year, the control is enforced Version 316 is less accurate. Apparently, the method of only for the region overall, and only average number of transforming the population estimate into the control workers per household is supplied. Therefore, the category induces bias in the forecast. forecast-year control is really quite weak. In the base Examination of base-year validation statistics for age year, the controlled worker categories are extremely categories of persons in the synthetic population shows accurate and precise, and uncontrolled subcategories are that controlling households by age of householder in noticeably less accurate and precise. In the back-cast, it is Version 316 may provide a small improvement in the apparent again that inaccuracy is induced by deriving accuracy and precision of person ages for the major cat- controls from averages, and the quality of the largest egories of 0 to 17, 18 to 64, and 65+. For detailed age uncontrolled category (three workers) is not worse than subcategories, results are unusably inaccurate and impre- the controlled categories. In addition, the use of the cise at the tract level; at the PUMA level, precision and regional control degrades tract-level precision. There accuracy are more acceptable. In the forecast year, Ver- would possibly be much to gain from trying to estimate sion 316 results differ from those of the other versions a distribution of households by number of workers but with similar accuracy and precision, and for all ver- rather than only an average number of workers per sions the quality degrades somewhat from the base year household, and the benefits would probably be much but not a lot. greater if this could be done for geographic units smaller than the region. The employment status of each person is also in the Family synthetic sample. In the base year, the categories of (a) employed civilian and (b) not in labor force are precise Family is controlled in Versions 128 and 316 but only in and accurate at the PUMA level, apparently because of the base year. In the base year, the controls improve pre- the household-based employment controls, although they cision and accuracy, but without the control, precision are extremely imprecise at the tract level. The back-cast and accuracy of Version 52 are still quite good, even at validation values taken from the census are incorrect (for the tract level. The base-year controls appear to have lit- a yet undetermined reason), so the validity of personal tle carryover effect in the forecast, in which the uncon- employment in the back-cast cannot be determined. trolled categories are no better in Versions 128 and 316 For employed persons, the category hours worked per than in Version 52. Precision remains fairly high, but week is also recorded in the synthetic population. The accuracy gets considerably worse. category working 35 or more hours per week is extremely accurate and precise, even at the tract level, in the base year and the back-cast. For the categories of 15 Housing Type and Ownership Status to 34 h per week and 1 to 14 h per week, the results are imprecise and inaccurate at the tract level but reasonably The accuracy and precision of these variables, which are accurate and precise at the PUMA level, in both the base completely uncontrolled in the base year and forecast, year and the back-cast. might nevertheless be considered good enough to be usable at the PUMA level of geography, except for the tiny category of mobile home dwellers. The tract-level Age results are too inaccurate and imprecise to be usable. Age is controlled only in Version 316, with three cate- gories on the basis of whether a householder is over or Gender under age 65 and, for those under 65, whether a house- holder's own children under the age of 18 are present. Although there are no controls related to gender, the For the forecast year, the control is supplied only as the number of males and females are fairly accurate and pre-