Mean number of times per lost message that a receiver transport transmitted
a NAK. (LBT-RM, LBT-RU)

- n (Int32)
- Statistics set index

Mean number of times per lost message that a receiver transport
transmitted a NAK.

Ideally this should be at or near 1. A higher value indicates a lossy
network. This is an exponentially weighted moving average (weighted to more
recent) for accumulated NAKs per lost message.
This method returns a value from the nth set of statistics
encapsulated within this object.