Performs a permutation test of differences in means between groups of censored data.
cenpermanova(y1, y2, grp, R = 9999, printstat = TRUE)
y1 | The column of data values plus detection limits. |
---|---|
y2 | The column of indicators, where 1 (or |
grp | Grouping or factor variable. Can be either a text or numeric value indicating the group assignment. |
R | The number of permutations used. Default is 9999. |
printstat | Logical |
Permutation test results with the number of permutations, range in test statistics and p-value
values through the various permutations. Group means are also listed.
Because this is a permutation test it avoids the problem with MLE tests (see cenanova
) that assume a normal distribution. No values are modeled as below zero and group means and p-values
are trustworthy.
Good, P., 2000. Permutation Tests: A Practical Guide to Resampling Methods for Testing Hypotheses, 2nd ed, Springer Series in Statistics. Springer-Verlag, New York, NY. doi: 10.1007/978-1-4757-3235-1
Helsel, D.R., 2011. Statistics for Censored Environmental Data using Minitab and R, 2nd ed. John Wiley & Sons, USA, N.J.
#> Permutation test of mean CensData: PbHeron$Liver by Factor: PbHeron$DosageGroup #> 9999 Permutations #> Test Statistic = 1122 to 1122 p = 0.0015 to 0.002 #> #> mean(High) mean(Low) #> 9.2880 0.1204