[R] Fw: Reversing data transformation

[Uwe Ligges]

On 06.04.2013 22:21, Beatriz González Domínguez wrote:
>
>
> From: aguitatierra at hotmail.com
> Sent: Friday, April 05, 2013 11:47 PM
> To: r-help at r-project.org ; R Help
> Subject: Reversing data transformation
>
> Hi everybody,
>
> I would be very grateful if you could give me your thoughts on the following issue.
>
> I need to perform  Box-Cox (bcPower€) transformation on my data. To do this, I calculated lambda using the function '€powerTransform'€.
>    powerTransform(data)

We get:

Error: could not find function "powerTransform"


so that fucntion appears to be from some not mentioned package.


> However, I got an error message when performing this function:
>    Convergence failure: return code = 52
> I was told by John Fox that the nature of my data was probably causing the problem so I applied the following transformation:
>    powerTransform(1e7*(data - 0.99*(min(data))))   [1]
 >
> And it worked! However, now when I try to check the normality of my data,
>    shapiro.test(data)
> I get a new warning message:
>    Error in shapiro.test(data) :
>      ifault=6. This should not happen
> I think this may be solved by removing the transformation I applied previously in [1], but I’m not sure how to do it properly.
>
> Could anyone give me some advice?
>
> MY DATA:
> c(0.000103113, 0.000102948, 0.000104001, 0.000103794, 0.000104628,
> 9.2765e-05, 9.4296e-05, 9.5025e-05, 9.4978e-05, 9.8821e-05, 9.7586e-05,
> 9.6285e-05, 0.00010158, 0.000100919, 0.000103535, 0.000103321,
> 0.000102842, 0.000102315, 0.0001033, 0.000103691, 0.000102689,
> 0.000103248, 0.000101216, 0.000103127, 0.000103439, 0.000102818,
> 0.000103482, 0.00010227, 0.000104264, 0.000104672, 0.000104586,
> 0.000104516, 0.000104585, 0.000103804, 0.000103702, 0.000103405,
> 0.000104815, 0.000101718, 0.000101792, 0.000103273, 0.000102942,
> 0.000102522, 0.000103149, 0.0001036995, 0.0001039735, 0.000101487666666667,
> 0.000102796)


shapiro.test on this data works for me:

         Shapiro-Wilk normality test

data:  data
W = 0.7314, p-value = 6.243e-08


Best,
Uwe Ligges

> Thanks a lot!!
>
> Bea
>
>
>
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