Stats Question

I am just learning the ways of BIND 9. I am new to dns. I have two dns
servers running with just a few people using them. I ran a rndc stats to
see how things were going. Contrasting what I am seeing in the book DNS
and BIND it looks like I have an inordinant number of nxdomain issues.

Here is the named.stats file:
+++ Statistics Dump +++ (1077898378)
success 540
referral 0
nxrrset 17
nxdomain 338
recursion 501
failure 0
--- Statistics Dump --- (1077898378)
+++ Statistics Dump +++ (1077912492)
success 611
referral 0
nxrrset 17
nxdomain 373
recursion 595
failure 0
--- Statistics Dump --- (1077912492)

Is this abnormal? If so, what do I look for?

Thanks,

Tom Naves