where P.^ is price for firm i at time t, B.^ is the reported book value, and X.^ is the reported
earnings." Variations of this regression appear in most 'Value relevance" studies.
Typically, the coefficients for this regression are estimated using cross-sectional or
panel data. Often Ohlson (1995) is cited by these studies as the motivation for including
both book value and earnings in this regression.
It is instructive to compare equation (2) to equation (5). The right-hand side of
equation (2) consists of the current book value and the present value of a stream of
expected future abnormal earnings. The right-hand side variables of equation (5), however,
consist of reported historical accounting numbers. Notice that several rather strong
assumptions about the way past earnings and book values map into future payoffs are
necessary to move from equation (2) to equation (5).