On Jun 7, 2012, at 7:30 AM, Mohan Radhakrishnan wrote:
Hi,
I am again asking a generic question and the general
response for such questions is cold. I am a beginner but use and
write simple R scripts.
Have you read the Posting Guide?
"If the question is well-asked and of interest to someone on the list,
it may elicit an informative up-to-date answer. See also the Usenet
groups sci.stat.consult (applied statistics and consulting) and
sci.stat.math (mathematical stat and probability).
Basic statistics and classroom homework: R-help is not intended for
these. "
There are other forums online for such questions:
stats.exchange.com is one such. (And I would have to say that the
Usenet group advice is seriously outdated.)
I am looking for some ideas to calculate the confidence
intervals based on this excerpt from the paper. Moreover it would
help if someone points to material to read about degrees of freedom
and any related concepts.
Now that last one is surely a sign of "failure to google".
--
David.
Thanks,
Mohan
Cutting Corners: Workbench Automation
for Server Benchmarking
APPENDIX: Confidence Intervals
Given N observations of response time from N runs at
given arrival rate λ, the confidence interval for the response
time at that λ with a desired confidence level, c%,
is computed as follows:
• Compute the mean server response time: μ =
PN
i=1 Ri/N, where Ri is the server response time
for the ith run.
• Compute the standard deviation for the server response
time: σ = qPN
i=1(Ri − μ)2/(N − 1).
• Confidence interval for the response time at confidence
100c% is given as: [μ − zpσ/√N, μ +
zpσ/pN], where p = (1 + c)/2, and zp is the quantile
of the unit normal distribution at p.
If N <= 30, we replace zp by tp;n−1, which is the pquantile
of a t-variate with n−1 degrees of freedom,
assuming that the response time values from N runs
come from a normal distribution. We verified that
response times do come from a normal distribution
using a normal proability plot.
DISCLAIMER:\ ===============...{{dropped:31}}
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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David Winsemius, MD
West Hartford, CT
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