Re: how are confidence intervals calculated?

Rick Jones (
Wed, 12 Aug 1998 20:36:51 PDT

> we frequently get messages like the following during TCP and UDP stream
> tests:
> TCP STREAM TEST to : +/-2.5% @ 99% conf. : interval
> !!! Desired confidence was not achieved within the specified iterations.
> !!! This implies that there was variability in the test environment that
> !!! must be investigated before going further.
> !!! Confidence intervals: Throughput : 39.7%

I don't fully understand the statistics myself, some folks at IBM did
the code, but in essence, it means that netperf was not confident (99%
probability) that the average throughput was closer than +/- 20% in
this instance.

Common causes of this are other things happening on the system(s),
other things happening on the network(s), bugs resulting in lost
packets, and so on.

rick jones