Quote from Doobs789:
Since I know you are a Livevol user; be aware that their proprietary indicators, such as IV30, is a weighted, hypothetical measure of the volatility of a rolling 30-day option. This differs from the volatility of an option of a discrete expiration cycle.
The measure of a stock's historical volatility, as mentioned in previous posts, will often include events, such as earnings, that will alter your measurement of a mean volatility, especially given the duration of the measurement. You have to decide if such events should be included in your measurement. Also, as sle mentioned, take into account the prevailing volatility climate for the period you are measuring (30% IV compared to 20% HV could be different from a relative standpoint with the VIX at 30, as opposed to 10). Therefore it is often quite difficult to make IV/HV bets. You can be right on with your prediction of volatility, and still lose money in many cases.
There could be some value in comparing different historical volatility measurement methods for a given time-frame, and placing your data into context with volatility cones. Or when looking at options of different expiration cycles, it can be useful to measure forward volatility (or the volatility the market implies between two dates).