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# Tag Info

I agree with Dan it is likely a typo. Some definitions (using your notations) Investment : $f_0$ Investment one year later : $f_1$ Net income : $f_1 - f_0$ ROI: $-1 + \frac{f_1}{f_0}$ It follows that the correct code should be ROI = (goog/goog.tshift(-365) -1)*100