Alex Speier had a really nice article in the Globe today regarding bullpens. If you haven't read it yet dgalehouse, I highly recommend it.
Here are some of the highlights:
"Of the 15 free-agent relievers who signed deals of at least $5 million per year, none was worth a single Win Above Replacement. Davis, Holland, Brandon Morrow, Jake McGee, Bryan Shaw, Tommy Hunter, Juan Nicasio, Addison Reed, Pat Neshek, Joe Smith, Anthony Swarzak, Steve Cishek, Luke Gregerson, Yusmeiro Petit, and Brandon Kintzler averaged 0.3 Wins Above Replacement."
AVERAGE ANNUAL VALUE (AAV) NUMBER AVERAGE WAR WIN PROBABILITY ADDED
$5M plus 15 0.3 -0.10
Minor league deal* 17 0.1 -0.03
"There were eight relievers who, after signing as free agents, were worth at least 1.0 WAR out of the bullpen, but none received one of the biggest contracts. The group was topped by Craig Stammen of the Padres (2.3 WAR, two-year, $4.5 million deal)"
And my personal favorite:
"Here’s a sobering thought for teams as they invest in relievers: The correlation coefficient between the average annual values of last year’s free agent relief class and those pitchers’ WARs was 0.002 — which is to say, there was no relationship at all between the money spent on big reliever deals and the performance of those relievers."
https://www.bostonglobe.com/sports/redsox/2019/02/11/looking-for-good-bullpen-investment-strategy-there-isn-one/sosV7rupp8ikAI5OuB0KOL/story.html