Should we be concerned?

No, that's not the new CD/download from some nouveau alt.folk artist.  This seems to be the new primary concern regarding the next ace of the Dodger pitching staff.  Or at least it seems that I have been observing an increase in mentions of the "Verducci Effect" and "Chad Billingsley" in the same sentence.  However, I wasn’t under the impression that Billingsley’s workload had increased by amount that should cause increased concern.  Eric Stephen touched on this thought as well here on TBLA, but I wanted to expand on it a little further.

What is the Verducci Effect?

Baseball Prospectus defines the Verducci Effect in their glossary this way:

Named for Tom Verducci of Sports Illustrated, this is a negative forward indicator for pitcher workload. Verducci, who called this the 'Year After Effect,' found that pitchers under the age of 25 who have 30-inning increases year over year tend to underperform. Will Carroll independently found that pitchers who break the "Rule of 30" tend to get injured. Carroll renamed this 'rule' the Verducci Effect in honor of the man who initially found the evidence.

Tom Verducci himself summarizes his idea in his own words (emphasis mine):

The unofficial industry standard is that no young pitcher should throw more than 30 more innings than he did the previous season. It's a general rule of thumb, ….

Pitchers generally feel the effects of abusive increases in workload the next year, not the season in which they were pushed. In other words, you might be able to finish that marathon for which you didn't properly train, but your body will have hell to pay for it. I call it the Year After Effect.

Here's the way I track it: Find major league pitchers 25-and-under who broke the 30-inning rule. In some cases a pitcher's innings the previous season may have been artificially depressed, such as by injury, so I'll use his professional high for the baseline, or…his college workload. All innings count (minors, majors, postseason).

How does the Verducci Effect apply to Billingsley?

Many of the references, like Beyond the Box Score point to Billingsley’s IP increase from 2007 to 2008 "147 IP last year, 212 this year – 65 inning increase", note 65 is a little more than twice 30, and stop there.  However, Billingsley’s innings pitched in 2007 were "artificially depressed" while he worked in a bullpen role for half the season.  If one uses his "professional high" in 2006 (163 IP) as the baseline instead, that is a 49 IP increase for last year instead, or 63% more than 30 IP, instead of 117% more.  Beyond the Box Score lists seven pitchers who are Verducci Effect candidates based on last year’s increases, and this adjustment puts Billingsley in family with the two lowest increases on the list. Tim Lincecum and Jair Jurrjens.

Consider Billingsley’s IP totals over time.  Again, Eric Stephen touched on this, but when viewed graphically, it’s pretty clear that 2007 is the outlier and that Billingsley’s innings pitched increase is pretty steady for his entire professional career, even if we tack on an estimated 230 IP for 2009.

Note: 2003 was his draft year, thus that is a partial-season following his season as a HS senior.

Also notice that for Verducci Effect purposes, his increases in IP from year to year show a slow and steady increase (dare we say well-planned?), 2007 notwithstanding:
12.00  /  17.00  /  -16.00  /  49.33

Furthermore, Billingsley has shown steady improvement in his pitch efficiency in his MLB career:
Pitches/IP    17.81    17.09    16.69
Pitches/7IP    124.68    119.62    116.80

The differences may not seem large, but at 2007 pitch rates, he would have completed five fewer innings in 2008.  This may make his 2008 increase more like 44 IP instead of 49.

Conclusions:

• Billingsley’s IP increase of 49 compared to his previous career-most is something to keep an eye on, but the red alert status of the 2007 to 2008 increase is a red herring when it comes to the Verducci Effect.
• If he had pitched 30 more innings in 2007, a season started in the bullpen and finished as a starter,  we wouldn’t even be having this discussion.
• We don’t know what extra work the Dodgers had Billingsley do during 2007 or the following off-season, if any.

As with all pitchers, especially young ones, injury is always a possibility and a risk, but it seems to me that, at worst, Chad Billingsley’s odds of injury or highly degraded performance are only slightly increased by the Verducci Effect.