Just to add to Greg's comments: I've previously used 'Earth Movers
Distance' to compare histograms. Note, this is a distance metric
rather than a parametric statistic (ie. not a test) but it at least
provides a consistent way of quantifying similarity.

It's relatively easy to implement the metric in R (formulating it as a
linear programming problem). Happy to dig out the code if needed.

Michael

On 13 October 2010 02:44, Greg Snow <greg.s...@imail.org> wrote:
> That depends a lot on what you mean by the histograms being equivalent.
>
> You could just plot them and compare visually.  It may be easier to compare 
> them if you plot density estimates rather than histograms.  Even better would 
> be to do a qqplot comparing the 2 sets of data rather than the histograms.
>
> If you want a formal test then the ks.test function can compare 2 datasets.  
> Note that the null hypothesis is that they come from the same distribution, a 
> significant result means that they are likely different (but the difference 
> may not be of practical importance), but a non-significant test could mean 
> they are the same, or that you just do not have enough power to find the 
> difference (or the difference is hard for the ks test to see).  You could 
> also use a chi-squared test to compare this way.
>
> Another approach would be to use the vis.test function from the TeachingDemos 
> package.  Write a small function that will either plot your 2 histograms 
> (density plots), or permute the data between the 2 groups and plot the 
> equivalent histograms.  The vis.test function then presents you with an array 
> of plots, one of which is the original data and the rest based on 
> permutations.  If there is a clear meaningful difference in the groups you 
> will be able to spot the plot that does not match the rest, otherwise it will 
> just be guessing (might be best to have a fresh set of eyes that have not 
> seen the data before see if they can pick out the real plot).
>
> --
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.s...@imail.org
> 801.408.8111
>
>
>> -----Original Message-----
>> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
>> project.org] On Behalf Of solafah bh
>> Sent: Monday, October 11, 2010 4:02 PM
>> To: R help mailing list
>> Subject: [R] compare histograms
>>
>> Hello
>> How to compare  two statistical histograms? How i can know if these
>> histograms are equivalent or not??
>>
>> Regards
>>
>>
>>
>>       [[alternative HTML version deleted]]
>
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