Forum Discussion
Does FORECAST.ETS.SEASONALITY work for anyone?
I took my original sheet and extend the input numbers to 3 full years, then ran FORECAST.ETS to estimate the first 3 months of the 4th year. They were silly: January showed a high number instead of low, February was low as it should be, then March was high again. It's like Excel was throwing darts.
The good news is that FORECAST.ETS.SEASONALITY did show a 12-month cycle, so you're right that the function needs at least 3 full years of data. (So it's not much use for startup companies.) The confidence interval from FORECAST.ETS.CONFINT showed an interval of 150, which might be a little high but is at least reasonable.
Yes, for the business with forecasting based on monthly results seasonality will always be 12 (or zero). However, that could be more useful cases like time peaks during the day for call center; availability of candidates on labour market during the year; even weather forecast, where seasonality function could be more useful.