[R] Data Censoring and Normality Tests

[Liaw, Andy]

I stand corrected!  Hope Bert doesn't mind me CC'ing the list.

Andy

> From: Berton Gunter
> 
> No Andy, they're (left) censored alright: their values are 
> known to be below
> 2.4, but not how far below. Truncated data "arise when 
> observations are
> actually observed only when they take on values in a 
> particular range (above
> 2.4, say). For observations outside that range, their EXISTENCE is not
> known." -- Meeker and Escobar, "Statistical Methods for 
> Reliability Data."
> 
> Cheers,
> Bert
>  
>  
> 
> > -----Original Message-----
> > From: r-help-bounces at stat.math.ethz.ch 
> > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Liaw, Andy
> > Sent: Tuesday, November 09, 2004 3:12 PM
> > To: 'Kenneth Frost'; r-help at stat.math.ethz.ch
> > Subject: RE: [R] Data Censoring and Normality Tests
> > 
> > I don't know much about censored data, but what you described 
> > doesn't sound
> > like censored data, but rather truncated data.  
> > 
> > I think normality tests are over-(ab)used, and would suggest 
> > inspection of
> > normal QQ plots instead (as you already do).  For formal 
> > tests, you might be
> > able to cook up something that test for truncated normality.
> > 
> > Cheers,
> > Andy
> > 
> > > From: Kenneth Frost
> > > 
> > > Hello,
> > > 
> > > I would like to know if there is a function in R that 
> will test for 
> > > normality and handle censored data sets.  Currently, I 
> > evaluate each 
> > > censored data set by the extent to which a normal scores plot 
> > > approximate a straight line.  For complete data sets I use 
> > > shapiro.test().
> > > 
> > > Below is an example of a censored data set.
> > > 
> > > data1<-c(0.00, 0.00, 0.00, 5.86, 5.17,  8.17,  5.12, 4.92, 
> > > 7.08, 5.73, 
> > > 5.44, 6.61, 6.34, 6.23, 5.97, 5.86, 5.15, 7.98, 6.72, 5.15, 
> > > 3.58, 6.86, 
> > > 6.12, 4.58, 6.07, 5.38, 5.21, 3.78)
> > > 
> > > The zero values occur because I cannot detect a pathogen 
> > with a value 
> > > below 2.4.  Using shapiro.test(), it seems that the data are 
> > > different 
> > > from a normal distribution.  However, the normal scores 
> > plot suggest 
> > > otherwise.
> > > 
> > > Using R version 1.9.1
> > > 
> > > Thanks in advance.
> > > 
> > > Ken
> > > ________________________________________________________
> > > Kenneth E. Frost
> > > Research Assistant
> > > University of Wisconsin - Madison
> > > Dept. of Plant Pathology
> > > 1630 Linden Dr.
> > > Madison, WI 53706
> > > kef at plantpath.wisc.edu
> > > 
> > > ______________________________________________
> > > R-help at stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide! 
> > > http://www.R-project.org/posting-guide.html
> > > 
> > >
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html
> > 
>