Well, good is highly subjective but there are sources of information.
I guess one of the problems is which identity and where was it applied? Here's a couple of thoughts that might get you closer to metrics.
So for enterprise you might try to look at Larry Ponemon's Cost of a Data Breach and attribute what amount were caused by theft of identity:
https://securityintelligence.com/media/2017-ponemon-institute-cost-of-a-data-breach-study/
For consumer, Symantec Lifelock seems to have commissioned the best/longest running study into this:
https://www.javelinstrategy.com/coverage-area/2017-identity-fraud
https://www.symantec.com/en/ca/about/newsroom/press-releases/lifelock-2016/lifelock_0202_01
https://www.symantec.com/en/in/about/newsroom/press-releases/lifelock-2017/lifelock_0201_01
https://www.lifelock.com/education/identity_theft_protection_vs_credit_monitoring/
Experian has a study but no info on sample size:
https://www.experianplc.com/media/news/2017/identity-theft-survey-results/
Lastly, Equinfax has given us the biggest real world study by a practitioner*...
http://money.cnn.com/2017/09/11/technology/equifax-identity-theft/index.html
* sorry, cheap shot I know, but I couldn't resist.
