Re: Distribution of a Percetile

You sort all the speeds from each distribution to see where 85% is. You
then compare to see if two groups are any different.

There are a lot of tests to determine whether the means (averages) are the
same for both group but no real test to see if both have identical 85th
percentile.

If you have data over several days for each group, then you could obtain the
85th percentile from each day and determine the distribution of that
measurement from before and after groups. In such case you are then testing
to see whether the mean 85th percentiles are significantly different from
two groups.

Ken

"Stephen Clark" <octopusuk@xxxxxxxxxxx> wrote in message
news:1127327998.99352.0@xxxxxxxxxxxxxxxxxxxxxxx
>I have some traffic speed data which consists of the speeds of individual
>vehicles as they pass a point on the road. These daily speed measurements
>(the sample size, n, is large but variable each day) can be charted and
>approximated with a skewed distribution.
>
> Some data was collected before and some after a change. I would like to
> obtain the distribution of the 85th%ile of these speed distributions and
> test whether they are the same.
>
> Can someone point me to a web resource which will allow me to conduct this
> test? Thanks.
>
>


.

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