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March 16th, 2013, 01:05 PM   #1
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Statistics: 90th percentile

I'm a little confused on how you would do something like this:

I have a cumulative probability distribution H(x):

0 0.31042
1 0.67825
2 0.89149
3 0.97196
4 0.9942
5 0.999
6 0.99985
7 0.99997
8 1

and I need to find the 90th percentile of demand..
I understand that this means its the minimum x so that H(x) >= 90% but I need an example to make sure I'm doing this right.
Would this mean x >= 3 in this case??
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March 17th, 2013, 12:40 PM   #2
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Re: Statistics: 90th percentile

It depends on whether x is a discrete variable or continuous. Your answer is correct for discrete. However if x is continuous you need to estimate (interpolation) what value of x corresponds to H(x) = 0.9.
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