Source: Board of Governors of the Federal Reserve System (US)  

Release: Seasonal Factors for Domestic Auto and Truck Production  

Units:  Seasonal Factor, Not Seasonally Adjusted

Frequency:  Monthly

A seasonal factor measures the percentage amount that on average, monthly production is above or below normal. A seasonal factor of 120 states that the month in question will usually be 20% above an average month's production level. Similarly, a seasonal factor of 100 implies an average month, while a factor of 80 implies a month that is typically 20% below average.

The not seasonally adjusted (NSA) data for auto assemblies are obtained from Ward's Communications, the weekly-basis seasonal factors (SFW), which contain adjustments for holiday and length-of-month effects as well as normal seasonal variation, and the number of production days, or weekdays in a month, are applied to MVAAUTOASN using the formula found here.