Do catchers call for more fastballs with a runner on first?

We've all heard it from everyone in baseball, announcers and field personnel alike: Players who are batting with a baserunning threat on first base will get more fastballs. It makes sense. A fastball gets to the plate quicker and gives the catcher more time to the throw out the would-be basestealer.

Let's take a look at how true it is.

Pitchers throw fastballs 61% of the time. With a runner on first, does that go up to 70%? What if the runner is a real speedster? Maybe it goes up to 75% or more?

The fact, and the surprise of the matter is, that while the fastball percentage goes up with a stolen base threat on first, it doesn't go up by much.

Here's the data:

Note: 2006 data (SB threat based on situations with a runner on first with second and third base open)

With a stolen base threat on first base (10 or more steals in 2006), the fastball percentage goes up marginally from 61.0% to 62.8%. With a major threat (30 or more steals), the percentage goes up a bit more to 63.2. It's a clear-cut trend, but not a very big one, or at least not as big as I thought it would be.