[R] Data Censoring and Normality Tests

[Liaw, Andy]

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
> 
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