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CFA Level I · CFA Level I Exam · Applications of Simple Linear Regression in Finance

Residuals from a linear regression of a company's earnings on time show a pattern of increasing, curved deviations, while earnings grow at a roughly constant percentage rate. The most appropriate response is to:

Earnings growing at a constant percentage rate follow an exponential path, which is linear in the log of earnings. Using ln(earnings) as the dependent variable in a log-lin model is therefore the most appropriate fix for the curved residual pattern.

  1. Aadd more observations to the linear model without changing its form.
  2. Buse the natural log of earnings as the dependent variable in a log-lin model.Correct
  3. Cuse the natural log of time as the independent variable in a lin-log model.

Explanation

Constant percentage growth implies exponential growth in earnings, which becomes linear in the log of earnings. A log-lin model, with ln(earnings) as the dependent variable, fits this pattern and typically removes the curved residuals. A lin-log model transforms the independent variable and suits a diminishing effect of X, and merely adding data does not fix a misspecified form.

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