[R] Probit Analysis

[Kjetil Brinchmann Halvorsen]

A better option for a confidence interval for LD50
might be Fiellers method. 

To see how to get the numbers from the object returned from dose.p, use for
example
str(object) or names(object).

Kjetil Halvorsen

-------Original Message-------

From: Ngayee J Law
Date: Tuesday, December 31, 2002 7:17:39 PM
To: apjaworski at mmm.com
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] Probit Analysis

Hi Andy,

Thanks! glm and dose.p can do exaclty what I want to do. Just a quick
question,
how can I extract the numbers in the glm.dose object created by the dose.p?
My
goal is to calculate a 95% CI for the 'LD50'.

- Jacqueline





apjaworski at mm 
m.com To: "Ngayee J Law" <Ngayee.Law at celeradiagnostics.com> 
cc: r-help at stat.math.ethz.ch 
12/31/2002 Subject: Re: [R] Probit Analysis 
02:47 PM 







Jacqueline,

This should be a simple application of GLM. Check the help pages for glm,
family and dose.p in library MASS. Look at the example at the bottom of
the dose.p help page - it does almost exactly what you need.

Hope this helps,

Andy

__________________________________
Andy Jaworski
Engineering Systems Technology Center
3M Center, 518-1-01
St. Paul, MN 55144-1000
-----
E-mail: apjaworski at mmm.com
Tel: (651) 733-6092
Fax: (651) 736-3122


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Hello all,

I have a very simple set of data and I would like to analyze them with
probit analysis.
The data are:

X Event Trial
100 8 8
75 8 8
50 6 8
25 4 8
10 2 8
0 0 8

I want to estimate the value of X that will give a 95% hit rate
(Event/Trial) and the corresponding
95% CI. Anyone can offer some help? Thanks!!

- Jacqueline

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