Adjusted ERA is often abbreviated to ERA+ (or ERA Plus)
A metric developed by Baseball Reference that is calculated, as follows:
League Average ERA+ is set to 100 and anything above or below that suggests a pitcher is better or worse than MLB Average, respectively.
FanGraphs also uses a similar metric they’ve developed, known as ERA- (or ERA Minus). Here is their summary of the metric:
While both of these stats are calculated differently, they ultimately answer the same question… “How good is a pitcher at preventing runs when we account for park & league effects?”
ERA+: The better the pitcher is at preventing runs, the HIGHER this number goes
ERA-: The better the pitcher is at preventing runs, the LOWER this number goes (thus, it can be assessed similarly to a traditional ERA i.e. the lower, the better).
***In both cases, MLB Average is set to 100.
If you would rather just stick to TRADITIONAL ERA, the full summary for that is HERE!!