Re: how are confidence intervals calculated?

Rick Jones (raj@cup.hp.com)
Wed, 12 Aug 1998 20:36:51 PDT

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In reply to: Roland Yeo: "how are confidence intervals calculated?"

> we frequently get messages like the following during TCP and UDP stream
> tests:
>
> TCP STREAM TEST to 137.132.12.226 : +/-2.5% @ 99% conf. : interval
> !!! WARNING
> !!! 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

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