Feeling buried by the daily onslaught of economic data? It's understandable. Not only do you have to consider information on the overall national economy like the U.S. current account, but you also need to keep pace with data on specific sectors of the economy that you choose to follow for personal or investment decisions.

For instance, if you've made a big bet on drug companies like Pfizer, you might want to make sure you have the latest information on retail pharmacy sales from sources like the IMS Retail Drug Monitor. If you prefer a biotech company like Genentech, on the other hand, you might want to peruse the Biotechnology Industry Organization's Guide to Biotechnology. Most industries have similar publications and releases of data that provide specific information of importance to people in those industries.

Among all the industries that make up the U.S. economy, only a few of them release data considered worthy of national attention. Many retailers release information about their sales, allowing investors to draw conclusions not only about the individual retail companies, but also the industry as a whole. Similarly, motor vehicle manufacturers disclose information about the number and types of vehicles they are selling on a monthly basis. Because cars and trucks are a constant presence in everyday American life, these figures have major implications for the health of the automotive industry and the domestic economy as a whole. Let's take a closer look at the way automakers report this information and how you can use it to understand the economy better.

The basic concept
The numbers that motor vehicle manufacturers release on sales are relatively straightforward. Typically, the manufacturer gives information on the number of vehicles sold during the month. The total number is then broken down by the particular brand; for instance, Ford (NYSE:F) provides sales numbers for Ford, Mercury, Lincoln, Jaguar, Land Rover, and Volvo (NASDAQ:VOLV). In addition, numbers of cars and trucks are presented separately, and further breakdowns by specific make and model provide helpful information on trends within the industry. Comparisons with figures from the same month of the previous year are also made available.

Because each automaker releases data separately, it's important to understand that the information will not necessarily come in a standardized format. Different companies may choose to release information in a slightly different way. For instance, General Motors (NYSE:GM) specifically refers to the number of sales days in a given month. This can be useful in drawing conclusions, because if a slight increase in sales occurs in a month with an extra day of sales, then it may be appropriate to conclude that actual sales were weaker and the way days fell on the calendar was the only factor allowing gross sales to increase. In addition, U.S. subsidiaries of foreign automakers, such as Toyota (NYSE:TM) and Honda (NYSE:HMC), usually provide information about whether the vehicles they sold came from American manufacturing plants or were imported from abroad.

Unlike information provided by impartial parties like government agencies and private research firms, data on auto sales comes straight from the auto companies. The information usually comes in the form of a press release that includes not only raw numbers but also statements from company executives highlighting certain portions of the data. Although some companies provide raw data in a table after the company statement, some intersperse the data within the commentary section (though this can sometimes make the data difficult to extract).

Economic implications
Clearly, the auto industry is a big player in the economy. With total gross revenue for Ford and General Motors each approaching $200 billion annually, the vehicle-manufacturing industry provides a substantial component of America's gross domestic product. Both Ford and GM have hundreds of thousands of employees working for them. Furthermore, all kinds of related industries rely on the automakers as a source of their own business. The fortunes of parts makers like Delphi rests on the success or failure of vehicle manufacturers to achieve their goals. Retailers of car parts, such as AutoZone, take advantage of the buzz generated by new models that motivates car owners to add enhancements.

Looking at the data, we can see that the current state of the vehicle manufacturers has many facets. Overall, sales of vehicles are roughly in line with levels from last year, but the results for the individual companies vary widely. Toyota and Honda have improved their sales from year-ago levels, increasing their total share of the U.S. market to about 25%. Ford and GM have remained mostly flat from last fall, retaining market share of about 43%. The big losers are DaimlerChrysler (NYSE:DCX) and Nissan (NASDAQ:NSANY), each of which faces significant declines in sales from last year's levels.

It's fascinating to watch the monthly sales data for responses to external factors like gas prices. As gas prices rose dramatically over the past year, sales of larger cars and SUVs began to fall, while smaller, more fuel-efficient cars became more popular. However, automakers have responded to these pressures by offering incentives for buyers of larger vehicles, and with the steep drop in prices at the pump in just the past month, it won't be surprising to see year-end sales of larger vehicles begin to pick up once more.

In summary, information about auto sales gives more than important information to investors in the automakers. With the large contribution the automakers make to the overall economy in terms of employment and manufacturing output, data that provides insight on the auto industry can also be used to make inferences about the direction of the economy. By keeping in touch with the health of the automakers, you can anticipate changes that will affect you and your portfolio.

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Fool contributor Dan Caplinger hasn't made the auto companies happy by keeping his 13-year-old convertible on the road so long. He doesn't hold positions in any of the companies mentioned in this article. The Fool's disclosure policy gives you a smooth ride.