What does 95th %tile mean?

Alex Pilosov alex at pilosoft.com
Fri Apr 20 13:57:55 UTC 2001

On Fri, 20 Apr 2001 Toby_Williams at enron.net wrote:

> _95th%ile is not a robust mechanism for billing_
>  It neither addresses variance nor average use effectively and can be gamed
> quite easily. It's some kind of best fit system for billing buyers with "normal
> behaviour".
> Where in maths class did they ever say that scraping off the highest n percent
> of a data set in isolation, gives a good indication of anything? Don't you need
> to look at the mean and 90th percentile together to fairly evaulate
> distribution.
> I think the reason it's so popular currently is that it's easy to describe
> (hence sell) and fits normal use reasonably well, so from a "normal buyer's"
> perspective is OK. Just as long as everyone is honest.
Absolutely. Here's a scheme that, if everyone was using only 95th
percentile billing, would give you webhosting at gigabit rate while only
paying 30x minimal rate webhosting:

a) colocate hardware at 30 different datacenters at gigE speed, but billed
for 95th percentile.
b) have a DNS server that rotates records, pointing to a different
server each day.
c) bingo. Each of your providers will remove highest 95th percentile (1.5
days worth of traffic) and only bill you for minimal utilization. 


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