The scale function seems to have tackled the skew, just looking at the
boxplots for the data.
The boxcox function I'm using is boxcox(), from MASS. I've looked through
the help page, but I don't think (from what I can see) there's a way to make
the boxcox function handle the negative values, unlike say the b.c function
(from car, I think), which has a 'start' argument.
How would I add, say, a constant c to each piece of data? Whilst I think I
understand the stats, I'm pretty terrible at manipulating R, as I've only
been using it for a few days!
Thanks again,
Henry
2009/11/30 David Winsemius <dwinsem...@comcast.net>
>
> On Nov 30, 2009, at 11:02 AM, Henry Thorogood wrote:
>
> Hi,
>>
>> I'm doing some work with linear models, and I've scaled my data using the
>> scale(dataset) function. This was great at removing the skew, but I now
>> can't perform the Box Cox transformation on the data set (using the
>> boxcox(dataset) function), as the scaling has returned negative values.
>>
>
> Scaling (at least that using the default approach with that function)
> should not "remove" skewness.
>
>
>
>> So my question is: how can I get the scale function to return a positive
>> set
>> of data (so I can use Box-Cox),
>>
>
> You could shift the scaled values to the right.
>
>
> or how can I get the boxcox function to
>> handle negative values.
>>
>
> Which boxcox function? And have you looked at all of its available
> parameters?
>
> --
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
>
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