My original handmade seasonal inventory adjustment is lost to the ages.

FORBES: U.S. Housing Inventory Update

But the forecasting firm Macroeconomic Advisers, which prepares the report with ADP, warned Wednesday that its estimate of December job growth might have been stronger than merited because of seasonal-adjustment problems specific to the ADP data set.

WSJ: What's Behind the Jobs Report?

No one I know has any idea as to how the BLS does this seasonal adjustment.

FORBES: Is Bureau Of Labor Statistics Data Skewed?

Here is the Department of Numbers series (which goes out to March) overlaid against the seasonal adjustment.

FORBES: U.S. Housing Inventory Update

One reason is that seasonal adjustment is tricky in such countries where the shift from agriculture to industry changes the pattern of seasonality over time, says Mr Kroeber.

ECONOMIST: Is China overstating its true rate of growth?