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ALTERNATIVE MODEL DESIGNS: PROGRAM PARTICIPATION FUNCTIONS AND THE ALLOCATION OF ANNUAL TO 96 MONTHLY VALUES IN TRIM2, MATH, AND HITSM the year. The result is an imputed employment history for each individual in the March CPS that records their labor force participation, unemployment, and employment status during each week of the income year. Comment All three models use complex procedures to determine monthly labor force status. However, each emphasizes different aspects of the variations in labor force activity that characterize the population throughout the year. The TRIM2 MONTHS routine uses information on the number of employers and spells of unemployment to simulate variable patterns of labor force status over the year. The results of the individual simulations are controlled to the seasonal variations and trends in aggregate employment and unemployment during the year as reported by the BLS. The MATH ALLOY routine makes use of ISDP results on employment status patterns within families to relate the work periods of husbands and wives (with the exceptions noted above of certain husband-wife families simulated to be eligible for AFDC). Otherwise, ALLOY takes a straightforward approach that does not allow for seasonal variations or for very complex patterns of individual labor force status during the year. HITSM, like TRIM2, makes use of the information on the number of jobs and spells of unemployment to allow for a variable pattern of employment status on an individual basis. HITSM also takes limited account of seasonal variations in its treatment of the employment patterns of students. Determination of Monthly Earnings Input Data The March CPS public-use files provide, for each person 15 years of age and older at the time of the March supplement interview, the following items pertaining to earnings during the preceding calendar year: annual income from wage and salary jobs, annual net income (or loss) from nonfarm self-employment, and annual net income (or loss) from farm self-employment. In addition, an hourly wage rate can be constructed for workers from annual earnings, number of weeks worked, and normal hours worked per week (the current hourly wage rate is also available for hourly workers for about one-fourth of the sample). TRIM2 The MONTHS routine first sums the annual earnings variables (income from