Income Growth Factors: Error Introduced through the Application of Cohort Data
指出，在计算未来收入现值时使用队列数据会忽略通货膨胀和未来生产率增长，导致低估收入增长，从而产生误差。
Numerous applications exist for the single dollar amount representing the present value of future (lifetime) earnings. In general, the present value of future earnings for a worker currently age x (PVJ) can be expressed as: e y )n-x e Y ( 1 + g)n PV x 2 (1 + .)l (1) n = x ( 1) where Yx is the average income at age Y, i is the assumed interest rate and g is the assumed annual growth rate of income; g is normally a constant for each x < n e where e is the worklife expectancy. Recent refinements in this formula have been directed toward claims that, in many cases, the use of a level annual rate of salary increase underestimates the present value of future earnings [2, 5, 9]. One of these refinements [2] argues that in a vast majority of occupations earnings increase much faster at the younger ages. Since these early earnings are affected to a lesser degree by interest discounts than are later earnings, the net result of the level growth assumption is an underestimation of the present value of all future earnings. While the methods devised to overcome this difficulty [2,5] recognize that earnings do not generally increase at a constant compound rate, they use cohort data in their computations (i.e., they use data from groups of people who are different ages at the same point in time.) Is it realistic, though, to assume that an individual age 30 today will, in another 30 years, be earning what another individual age 60 is earning in the same occupation today? There are at least two fundamental components of economic growth which are not considered when this assumption is used. The first is inflation the changing value of compensation. A more critical omission than the impact of inflation, which can be adjusted for explicitly, is that no allowance is made for general gains in productivity over the lifetime of the worker. Inherent in the cohort data are general productivity gains of past generations and productivity which has been acquired with age (experience); however, the assumption implicit in the use of cohort data in present value calculations is one of zero gain in general productivity in the future.