well , im not sure , but just found this document
https://forums.juniper.net/jnet/attachments/jnet/switch/1676/1/Key%20Performance%20Indicators%20for%20Juniper%20Devices%20version%202%202.pdf
its about EX4200 series .. not sure about other EX series
https://forums.juniper.net/jnet/attachments/jnet/switch/1676/1/Key%20Performance%20Indicators%20for%20Juniper%20Devices%20version%202%202.pdf
its about EX4200 series .. not sure about other EX series