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:

$$\overline{R_{a}} \cdot scale$$