Yesterday, Hot Air’s Ed Morrissey wrote that two conservative groups are charging that Andrew Stern, president of the Service Employees International Union, should have registered (or re-registered) as a lobbyist. They’re citing White House visitor logs (Stern was the most frequent visitor in the fist batch of records released) and his own tweets as evidence.

The same day, Washington Post reported that the U.S. Chamber of Commerce is trying to raise $50,000 to commission an economist to find fault with current health care reform proposals working their way through the Senate.

Without speculating on whether Stern should have registered to lobby, it’s worth noting that those who fail to disclose are not prosecuted and rarely fined. Without speculating on whether it’s unusual for trade groups to commission studies that will support whatever position they’ve taken on an issue, it’s worth noting that whether or not producing such a report and getting hundreds of other economists is a federal lobbying expense depends on which of three definitions of lobbying an organizations chooses to use when filing its disclosures.

As previously noted, different organizations use different definitions of lobbying when calculating what they’re spending to influence the government. Under one of the definitions, attempts to influence state elections and grass roots lobbying count as reportable federal lobbying expenses; under another, lobbying is defined as contacting federal officials in the executive branch, members of Congress and their staffers, and “efforts in support of such contacts, including preparation and planning activities, research and other background work that is intended, at the time it is performed, for use in contacts, and coordination with the lobbying activities of others.”

The images above and below illustrate the disparities that these differing definitions produce. Using the broadest definition, the Chamber reports millions in lobbying spending (above) while the SEIU, which uses a narrower definition, reports spending hundreds of thousands of dollars.

SEIU and the Chamber are on opposite sides of just about every major legislative battle going on in Congress. Just looking at the disclosure forms, it would appear that the former is far outspent by the latter, but if they filed using the same definition, that gap would shrink considerably.

Consider that SEIU is a big player in state elections, has an active federal political action committee and engages in a lot of grassroots lobbying. When the Chamber engages in those activities, the expenses for them are reflected in the expenditure figure they report. The SEIU doesn’t reflect those expenses in its expenditure figures.

The real problem is that neither number itemizes the spending. As an experiment, Real Time will take a stab at doing that–at breaking down the Chamber’s number using various sources of disclosure–including OpenSecrets.org, FollowTheMoney.org, and other disclosure tools. We’ll also attempt to construct a comparable number for SEIU using the same disclosures, and work our way around the obvious flaws in lobbying disclosure (the numbers are either apples, oranges or pears, except when they’re bananas) to arrive, if we can, at a single influence number that can be used for comparison.