an xts, vector, matrix, data frame, timeSeries or zoo object of
asset returns
scale
number of periods in a year (daily scale = 252, monthly scale =
12, quarterly scale = 4)
geometric
utilize geometric chaining (TRUE) or simple/arithmetic chaining (FALSE) to aggregate returns,
default TRUE
Details
Annualized returns are useful for comparing two assets. To do so, you must
scale your observations to an annual scale by raising the compound return to
the number of periods in a year, and taking the root to the number of total
observations:
$$prod(1+R_{a})^{\frac{scale}{n}}-1=\sqrt[n]{prod(1+R_{a})^{scale}}-1$$
where scale is the number of periods in a year, and n is the total number of
periods for which you have observations.
For simple returns (geometric=FALSE), the formula is:
$$\overline{R_{a}} \cdot scale$$
References
Bacon, Carl. Practical Portfolio Performance Measurement
and Attribution. Wiley. 2004. p. 6