Re: [R] How to test significant differences for non-linearrelationships for two locations

From: Jenny Sun <jenny.sun.sun_at_gmail.com>
Date: Tue, 27 May 2008 00:10:35 -0600

Thanks for the reply!

I thought of dummy variable. But I have no idea how to put the dummy into the model.

Say I have a Y~ X relationship in logistic form as:

nls(Y~a/(1+b*exp(-c*X),start=c(a=1,b=1,c=1) assume I am using nls to solve the question.

where could I put the dummy variable? Thanks!

Jenny

> is it possible for you to include the site as a dummy 0-1 and then
>use just one logistic model rather than two ? this way, the test of
>whether site
>matters would be easier to do using say a likelihood ratio test of the
>full model versus sub model. then, if the site dummy is significant,
>that
>means the relationships for the two sites are significantly different.
>
>
>
>
>On Tue, May 27, 2008 at 2:23 AM, Jenny Sun wrote:
>
>> Hi List,
>>
>> I have to compare a relationship between y and x for two locations. I
>> found logistic regression fits both datasets well, but I am not sure
>> how to test if relationships for both sites are significantly
>> different. I searched the r site, however no answers exactly match the
>> question.
>>
>> I used Tukey's HSD to compare two means, but the relationship in my
>> study was not simply linear. So I was wondering if there is anyone had
>> experience in making such comparisons. Thanks in advance!
>>
>> Jenny
>>
>> [[alternative HTML version deleted]]
>>
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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 27 May 2008 - 06:36:41 GMT

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