[R] offlist comment Re: KS Test question (2)

[David Winsemius]

On Aug 5, 2010, at 4:10 AM, Ralf B wrote:

> This is unbelievable. Now people like yourself start doing background
> searches on one and accusing one of not being professional

Your words, not mine.

> plus posting cheeky R code.

It appeared that you were having problems and did not have an  
efficient strategy for searching the archives, so I shared with you  
code that I developed and have put in my .Rprofile setup file. I do no  
see where that is "posting cheeky R code". I saw it as trying to be  
constructive. Using it would only be part of the recommended actions  
to take before posting


> The reason why I submitted the questions I have
> submitted was that these answers did not satisfy my particular problem
> (or perhaps I mistakenly thought so). The point here is that the forum
> should be a forum where one should be allowed to ask questions without
> first studying the history of the the entire forum in fear that
> someone might have asked it before.

If you read the Posting Guide I think you will find precisely the  
opposite expectation explicitly presented. Using my "cheeky code"  
would only be part of the recommended actions to take before posting  
if you follow the recommendations of the "Do your homework before  
posting:" section. This list was not set up to be a chat room or a  
tutoring center for general questions in statistics.

While you are reading the Posting Guide, please note that it expresses  
this advice regarding posting messages that were sent privately:

"Take care when you quote other people's comments to respect their  
rights, e.g., as summarized here. In particular
	
	• Private messages should never be quoted without permission,  "


> I was hoping that I could find
> clearer answers then what I was able to read. I do know how to search
> in Google. But I am not an expert in statistics, as you already found
> in your background check. If I would be fluent in stastitsics and R
> and if past answers would have exactly satisfied my problem I would
> not post here and I certainly would not have occupied your expensive
> attention.
>
>
>
>
>
> On Wed, Aug 4, 2010 at 6:16 PM, David Winsemius <dwinsemius at comcast.net 
> > wrote:
>>
>> On Aug 4, 2010, at 5:49 PM, Ralf B wrote:
>>
>>> Hi R Users,
>>>
>>> I have two vectors, x and y, of equal length representing two  
>>> types of
>>> data from two studies. I would like to test if they are similar  
>>> enough
>>> to use them interchangeably. No assumptions about distributions  
>>> can be
>>> made (initial tests clearly show that they are not normal).
>>> Here some result:
>>>
>>> Two-sample Kolmogorov-Smirnov test
>>>
>>> data:  x and y
>>> D = 0.1091, p-value < 2.2e-16
>>> alternative hypothesis: two-sided
>>>
>>> Warning message:
>>> In ks.test(x[1:nx], y[1:nx], exact = FALSE) :
>>>  cannot compute correct p-values with ties
>>>
>>> Here some questions:
>>>
>>> a) What does the error message means and what does it imply?
>>> b) The data is very noisy and the initial result shows that there is
>>> no relation between x and y. Is there a way to calculate and effect
>>> size?
>>> c) Can the p-value be used, when running tests over a large amount  
>>> of
>>> different data sets, as a metric for ranking similarity between x  
>>> and
>>> y data sets?
>>
>> There has been quite a bit of discussion on this list over the  
>> years about
>> why KS test is not good in this situation. If I read the results of  
>> a search
>> on your name correctly, you are in a department of Information  
>> Sciences. I
>> would have thought that the first reaction of someone in that field  
>> would be
>> do do a search on a question. Why are you filling up the archives  
>> with
>> questions that have been repeatedly asked and  answered?
>>
>> Do you need help in this area?
>>
>> rhelpSearch <- function(string,
>>                  restrict = c("Rhelp10", "Rhelp08", "Rhelp02",  
>> "functions"
>> ),
>>                  matchesPerPage = 100, ...)
>>         RSiteSearch(string=string,  restrict = restrict,   
>> matchesPerPage =
>> matchesPerPage, ...)
>>
>>
>> rhelpSearch("KS.test ties p-value")
>>
>>>
>>> Best
>>> R.


-- 
David Winsemius, MD
West Hartford, CT