These are percentiles. During a call values for each of the metrics (Jitter, Packet loss, etc.) vary with each voice data packet transmitted and are represented as percentiles.

 A 30% value of Jitter 45ms means out of all Jitter values that occurred during the course of call (with each voice data packet), 30% are less than or equal to 45ms, that is 30% of your call had Jitter less than or equal to 45ms.