how are confidence intervals calculated?

Roland Yeo (
Thu, 13 Aug 1998 10:07:28 +0800 (SGT)


does anyone know how are "confidence intervals" calculated in Netperf?

we frequently get messages like the following during TCP and UDP stream

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%
!!! Local CPU util : 0.0%
!!! Remote CPU util : 0.0%

Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec

57344 57344 32768 60.05 58.08

we would like to understand the calculations that go on in the background.

thanks for your advise.


Roland Yeo <> 
SingAREN, Centre for Internet Research, National University of Singapore