Bad Seasonal Adjustments

Several web sites have referred to "bad seasonal adjustment" or "bad seasonal adjustment combined with inclement weather in late December" as the cause for the increase in unemployment claims or problems with the payroll numbers.

Sometimes I take the phrase "bad seasonal adjustment" as a criticism of the seasonal adjustment software or the people who set the options in the seasonal adjustment software. I have to remind myself, though, that most people think about any kind of seasonal adjustment like it's a black box. So I suppose that a bad seasonal adjustment means that there is an extreme seasonal factor for that particular month so that the changes to the seasonally adjusted series from the raw series will also be extreme.

And if there was unusual weather in December that was causing something unusual to happen in the time series, then the seasonal adjustment software will take this into account.

Maybe I take it too personally. I looked at the seasonal adjustments for payroll, and all the factors and all the diagnostics, and it all looked really good to me.