Though the gleaming K Street buildings and high-profile hires of Washington’s government relations firms suggests business is booming, the amount of money officially disclosed as lobbying spending continues to decline -- at least, on paper.

In 2013, reported lobbying spending hit a five year low, according to the Center for Responsive Politics, falling to $3.24 billion from the previous record of high of $3.55 billion in 2010. And the data available so far suggests that disclosed lobbying expenses in 2014 may continue the downward trend.

Many analysts cite congressional gridlock as a cause. The Washington Post and others have reported this year on another possible explanation: The growing trend toward soft lobbying. In other words, a good chunk of lobbying activity – like campaign activity – has gone dark, which leaves expenditures invisible to the public or to regulators.

And so what looks like a decline may actually be an increase: Interviews and reports on individual companies suggest that the seeming drop in official lobbying is more than offset by an increase in money spent on other less overt forms of influence peddling.

Disputes over issues ranging from implementation of the Affordable Care Act, to the health effects of using various sweeteners, to Argentina’s debt dispute with U.S. hedge funds are increasingly waged by way of resources poured in to non-profit groups, think tanks and pop-up grassroots organizations, which are not subject to federal disclosure rules. The reluctance of the Obama administration to hire lobbyists to executive branch positions may have also contributed to a decline in the number of lobbyists who choose to formally register themselves that way -- though not in the actual activity.

Still, through the second quarter of this year, clients have spent an estimated $1,623,000,000 on lobbying, just $4 million less than what they spent through the first half of 2013.

On the legislative side, the same period has seen several of the most disliked, gridlocked, and unproductive Congresses in American history. Is a Congress that can’t pass bills to blame for lower lobbying revenues? If so, do lobbying expenses increase when Congress is productive?

The results are “a decidedly mixed bag,” writes Sarah Bryner, who oversees data analysis for CRP. Her study acknowledges the difficulty of measuring “productivity” over the two-year term of a specific Congress: Simply counting the number of bills passed fails to acknowledge the reality that many are ceremonial, such as adding new and exciting names to government buildings -- and the fact that a single, omnibus spending or regulation bill like the Affordable Care Act can have far more impact than a slew of smaller pieces of legislation.

Seeking a useful analysis, CRP created a model which measured the statistical significance of a diverse set of variables ranging from congressional disapproval ratings to whether Congress was divided. Out of these variables, only “whether earmarks were allowed” proved to have a significant relationship to the amount of money spent on lobbying. In other words, the ability for lobbyists to nail down specific earmarks affects annual lobbying spending, while the total number of bills passed does not.

Then again: the year's depressed total is still likely to surpass $3 billion -- a figure that dwarfs the $1.57 billion spent on lobbying in 2000.