In reply to Mark Rogers.

Hi Mark,

I've always used the most recent full year of available data (52 weeks or 12 months), although I suppose there is no harm in using a full 2 years or a full 3 years if you have it available. Using full yearly cycles is probably best, so as not to contaminate the CV calculation using only certain periods that are more or less volatile.

If you are using more granular time buckets, such as 15-minute increments which you might for electric utility demand or retail labor staffing, it might be more appropriate to calculate CV over a weekly cycle.

There is no hard rule here. Just calculate CV over the most appropriate time frame to represent what you are trying to forecast.