John D. Rackey, Lauren C. Bell, and Kevin R. Kosar at The Washington Post:

In ournew research, we collect and code every identifiable witness who appeared before every standing committee in the U.S. House of Representatives between 1971 and 2016, accounting for 435,293 witnesses appearing in 42,509 hearings over that 45-year period. Several patterns emerge from the data.  First … the number of witnesses appearing before Congress has sharply declined in recent decades. That number peaked in the 95th Congress (1977-1978), when House panels heard from 32,898 witnesses. By the 114th Congress (2015-2016), the number declined by nearly 80 percent, so that panels heard from only 6,632 witnesses.

Second, congressional hearings feature fewer witnesses on average today than they did in the past. In the 95th Congress (1977-1978), Congress heard from an average of 17.1 witnesses per hearing; by the 114th Congress (2015-2016), only 4.2 witnesses on average appeared. Recent scholarship and our own data suggest that witness appearances continue to fall. In the House Financial Services Committee, for example, the average number of witnesses per hearing fell to 3.7 during the 115th Congress (2017-2018) from 4.5 in the 114th Congress (2015-2016).

Declining witness participation cannot be explained by tumbling numbers of committee hearings or bills introduced. =..[A]lthough lawmakers introduced more bills during the 114th Congress than in the previous Congress, panels still heard from fewer witnesses than in the session before.

So, what are lawmakers doing instead of hearing from witnesses? They’re taking the limelight for themselves in ways that bring coverage in the news media. The media pays attention when a Cabinet secretary, a celebrity, or a well-known business tycoon appears before a congressional committee. But even congressional hearings on more-mundane policy matters can make the news when there’s a particularly heated exchange between legislators or when a legislator berates a witness or makes exceptional use of questioning time.