(一)(2)Ou and Penman use several independent variables(ROA,ROE,debt / equitydividend ratio,payout,gross margin ratio)that individually seem likely toproxy for expected returns。They also use several differenced variables(change in inventories,change in debt / equity ratio,change in ROE,growthin total assets)that individually seem likely to change in expected proxy forreturns,thus increasing the difficulty of controlling for post - announcementdifferences in expected returns on the long and short position - stocks。28When a combination of 16或18 such variables is selected from a set of 68。combined proxy for their potential to expected returns and changes inexpected returns is magnified。
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