Performs a permutation test of differences in means between two groups of censored data.
cenperm2(y1, y2, grp, R = 9999, alternative = "two.sided", 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 |
alternative | indicates the alternative hypothesis and must be one of " |
printstat | Logical |
Permutation test results with the number of permutations, range in group means and their difference, and range in p-value
.
Because this is a permutation test it avoids the problem with MLE tests (cen2means
) that assume a normal distribution. No values are modeled as below zero and p-values
are trustworthy. Ranges in means and p-values are due to interval-censoring of censored data means.
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.
Shapiro, S.S., Francia, R.S., 1972. An approximate analysis of variance test for normality. Journal of the American Statistical Association 67, 215–216.
#> Permutation test of mean CensData: PbHeron$Liver by Factor: PbHeron$DosageGroup #> 9999 Permutations alternative = two.sided #> mean of High = 9.288 to 9.288 mean of Low = 0.1093 to 0.1207 #> Mean (High - Low) = 9.179 to 9.167 p = 0.0013 to 0.0014 #>