[R] How to solve this problem ?

[Mark Difford]

Hi Daren,

>> Small progress, ...

m4 <- list(m1=m1, m2=m2, m3=m3)
boxplot(m4)

It's always a good idea to have a look at your data first (assuming you
haven't). This shows that the reliable instrument is m2.

HTH, Mark.


Daren Tan wrote:
> 
> 
> Small progress, I am relying on levene test to check for equality of
> variances. Is my understanding correct, the larger the p-value, the more
> likely the variances are the same ?
> 
>> trt
>  [1] 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4
> Levels: 1 2 3 4
>> levene.test(rep(rnorm(5), 4), trt, option="median")
> 
>         Modified Robust Brown-Forsythe Levene-type test based on the
> absolute
>         deviations from the median
> 
> data:  rep(rnorm(5), 4)
> Test Statistic = 0, p-value = 1
> 
> 
> 
>> From: daren76 at hotmail.com
>> To: r-help at stat.math.ethz.ch
>> Subject: How to solve this problem ?
>> Date: Wed, 20 Aug 2008 13:33:23 +0000
>>
>>
>> I have disabled html text editing mode, thanks to Prof. Ripley for the
>> kind reminder.
>>
>> Given three geological devices that takes 5 readings at 4 environmental
>> conditions (A to D). What will be the proper approach to select the most
>> reliable device ?
>>
>> m1 <- c(73,52,49,53,83,43,58,94,53,62,75,66,41,72,70,75,57,59,85,84)
>> m2 <- c(31,38,30,35,36,26,27,38,22,31,24,35,36,31,38,33,32,28,33,30)
>> m3 <- c(65,57,36,40,36,30,40,34,37,40,33,33,37,29,37,37,30,33,40,35)
>>
>> names(m1) <- rep(LETTERS[1:4], each=5)
>> names(m2) <- rep(LETTERS[1:4], each=5)
>> names(m3) <- rep(LETTERS[1:4], each=5)
>>
>> Before writing this email, I have tried to compare the sd for each device
>> at each condition, but ran into obstacle on how to formulate the null
>> hypothesis. Alternative solution tried was ANOVA, I am unsure whether it
>> can help, as it compares the differences in means of each group.
>>
>> Thanks
>>
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> 
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