These are percentiles. Call values for each of the metrics (Jitter, Packet loss, etc.) vary with each voice data packet transmitted; these are represented as percentiles. A 30% value of Jitter 45ms means out of all Jitter values that occurred during the course of a call (with each voice data packet), 30% of the values are less than or equal to 45ms. That means 30% of your call had Jitter less than or equal to 45ms.