# negatively skewed data; reflecting

6 messages
Open this post in threaded view
|

## negatively skewed data; reflecting

 Hi, This problem may be very easy, but I can't think of how to do it.  I have constructed histograms of various variables in my dataset.  Some of them are negatively skewed, and hence need data transformations applied.  I know that you first need to reflect the negatively skewed data and then apply another transformation such as log, square root etc to bring it towards normailty. How is it that I reflect data in R?  I'm sorry if this seems a very simple task, I think it involves going back to Maths GCSE and relearning reflection, rotation, translation etc!  I have searched the internet, but cannot come up with anything useful on how to reflect data. > hist(Lsoc)  #how do I reflect Lsoc in R? I am grateful for any help regarding this matter, it is just a very small part of my analysis and doesn't seem worth agonising hours over.  I will probably kick myself when someone tells me the answer! Thank you very much, Zoe ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
Open this post in threaded view
|

## Re: negatively skewed data; reflecting

 I'm new to R myself, but am wondering whether the t() (transpose) function would work? > hist(t(Lsoc)) Jon -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of [hidden email] Sent: 23 August 2006 13:08 To: [hidden email] Subject: [R] negatively skewed data; reflecting Hi, This problem may be very easy, but I can't think of how to do it.  I have constructed histograms of various variables in my dataset.  Some of them are negatively skewed, and hence need data transformations applied.  I know that you first need to reflect the negatively skewed data and then apply another transformation such as log, square root etc to bring it towards normailty. How is it that I reflect data in R?  I'm sorry if this seems a very simple task, I think it involves going back to Maths GCSE and relearning reflection, rotation, translation etc!  I have searched the internet, but cannot come up with anything useful on how to reflect data. > hist(Lsoc)  #how do I reflect Lsoc in R? I am grateful for any help regarding this matter, it is just a very small part of my analysis and doesn't seem worth agonising hours over.  I will probably kick myself when someone tells me the answer! Thank you very much, Zoe ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code. ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
Open this post in threaded view
|

## Re: negatively skewed data; reflecting

 In reply to this post by z.dalton On 8/23/2006 8:08 AM, [hidden email] wrote: > Hi, > > This problem may be very easy, but I can't think of how to do it.  I have constructed histograms of various variables in my dataset.  Some of them are negatively skewed, and hence need data transformations applied.  I know that you first need to reflect the negatively skewed data and then apply another transformation such as log, square root etc to bring it towards normailty. How is it that I reflect data in R?  I'm sorry if this seems a very simple task, I think it involves going back to Maths GCSE and relearning reflection, rotation, translation etc!  I have searched the internet, but cannot come up with anything useful on how to reflect data. > >> hist(Lsoc)  #how do I reflect Lsoc in R? Reflected <- -Lsoc will reflect about zero. > I am grateful for any help regarding this matter, it is just a very small part of my analysis and doesn't seem worth agonising hours over.  I will probably kick myself when someone tells me the answer! Please don't kick yourself :-) Duncan Murdoch > > Thank you very much, > > Zoe > > ______________________________________________ > [hidden email] mailing list > 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. ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
Open this post in threaded view
|

## Re: negatively skewed data; reflecting

 In reply to this post by z.dalton [hidden email] wrote: > Hi, > > This problem may be very easy, but I can't think of how to do it.  I have constructed histograms of various variables in my dataset.  Some of them are negatively skewed, and hence need data transformations applied.  I know that you first need to reflect the negatively skewed data and then apply another transformation such as log, square root etc to bring it towards normailty. How is it that I reflect data in R?  I'm sorry if this seems a very simple task, I think it involves going back to Maths GCSE and relearning reflection, rotation, translation etc!  I have searched the internet, but cannot come up with anything useful on how to reflect data. > >> hist(Lsoc)  #how do I reflect Lsoc in R? > > I am grateful for any help regarding this matter, it is just a very small part of my analysis and doesn't seem worth agonising hours over.  I will probably kick myself when someone tells me the answer! > > Thank you very much, > > Zoe To add further complication, if the transformation to normality is empirically based, the true variance of resulting estimates will inherit the variance from the empirical assessment.  For example, if you use a histogram or empirical CDF to find the transformation, the imprecision of the empirical CDF will add a good deal of true variance to the final estimates so that they are no more precise than sample quantiles on the original scale.  To put it another way, the sample median seems to be inefficient (efficiency 2/pi) compared to the sample mean if normality holds, but that relative efficiency rises if normality were "rigged". -- Frank E Harrell Jr   Professor and Chair           School of Medicine                       Department of Biostatistics   Vanderbilt University ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code. Frank Harrell Department of Biostatistics, Vanderbilt University