[R] NADA package/cenboxplot() method: maximum censored percentage

[David Winsemius]

On Aug 20, 2012, at 9:22 AM, Rich Shepard wrote:

> On Thu, 16 Aug 2012, David L Lorenz wrote:
>
>> The cenboxplot function uses cenros to estimate the censored  
>> values. The
>> cenros function requires at least 2 uncensored observations to be  
>> able to
>> do the regression. The cenros function does issue a warning when  
>> there are
>> more than 80% censored data, but that is suppressed in cenboxplot.
>
>  There must be something other than > 2 uncensored observations in  
> my data
> that prevent cenboxplot from functioning. For example, dissolved  
> arsenic
> concentrations have 578 total observations. Of these, 180 (31.14%) are
> censored and 398 are uncensored. Both number of uncensored  
> observations and
> the percentage of censored observations appear to be well within  
> plotable
> limits, but cenboxplot() returns this error:
>
> cenboxplot(as.d$quant, as.d$ceneq1, as.d$era, range=1.5,  
> main='Dissolved
> Arsenic', ylab='Concentration (mg/L)', xlab='Time Period')
> Error in if ((length(obs[censored])/length(obs)) > 0.8) { :
>  missing value where TRUE/FALSE needed
>
>  I would like to understand how the function obtains a censored  
> ratio > 0.8
> when it is actually 0.3114.

I see no evidence from what you have posted that the function "obtains  
a censored ratio > 0.8". The error messages says there were missing  
values. You might consider looking at :

table(Q=is.na(as.d$quant), CE=is.na(as.d$ceneq1), ERA=as.d$era)

My guess is that this test is failing for one or more categories of  
as.d$era.

>  Displaying the data frame, as.d, has a logical TRUE or FALSE for  
> each row;
> it can be provided if needed.

You could use dput() and post through Nabble, which would let people  
download if they were interested. Seems on the large size to be  
considered "minimal" .

-- 

David Winsemius, MD
Alameda, CA, USA