Since earnings management studies almost invariably examine samples of
firms that have experienced unusual performance, the most relevant conclusion
from Dechow et al.(1995) is that the discretionary accrual models are seriously
misspecified.The misspecification arises because the magnitude of normal
accruals, i.e., non-discretionary or expected accruals, is correlated with past
(and contemporaneous) firm performance.The dependence arises for two
reasons.First, as discussed in Section 4.1 on the time-series properties of
earnings, firm performance conditional on past performance does not follow a
random walk.Second, both operating accruals and operating cash flows are
strongly mean reverting (see Dechow (1994) for evidence, and Dechow et al. (1998a, b) for a model that explains the correlation structure), which means
these variables are not serially uncorrelated.How ever, none of the five
discretionary accrual models used in the literature explicitly captures accruals’
serial correlation property, so estimated discretionary accruals are biased and
contaminated with non-discretionary accruals.Eviden ce in Guay et al.(1996) ,
who use market-based tests, and Hansen (1999), who examines the behavior of
future earnings, suggests that the extent of the non-discretionary accrual
component in estimated discretionary accruals is large.Thom as and Zhang’s
(1999) conclusion is still stronger.They infer that the commonly used models
‘‘provide little ability to predict accruals’’.