Performs a parametric test of differences in means between groups of censored data, followed by a parametric Tukey's multiple comparison test.

cenanova(x1, x2, group, LOG = TRUE, printstat = TRUE)

## Arguments

x1 The column of data values plus detection limits The column of indicators, where 1 (or TRUE) indicates a detection limit in the y1 column, and 0 (or FALSE) indicates a detected value in y1. Grouping or factor variable. Can be either a text or numeric value indicating the group assignment. Indicator of whether to compute tests in the original units, or on their logarithms. The default is to use the logarithms (LOG = TRUE). To compute in original units, specify the option LOG = FALSE (or LOG = 0). Logical TRUE/FALSE option of whether to print the resulting statistics in the console window, or not. Default is TRUE.

## Value

Returns the Maximum Likelihood Estimation (MLE) comparison results including Chi-Squared value, degrees of freedom and p-value of the test. Test assumes log-normal(LOG=TRUE) or normal(LOG=FALSE) distribution of residuals from group means.

Tukey's multiple comparison p-values of pairwise differences in group means are also printed.

• Group Names of groups (NOTE: == 0 indicates null hypothesis of "equals zero").

• Estimate Estimated difference between group means.

• Std. Error Standard error of estimate.

• z value Test statistic.

• Pr(>|z|) P-values for test that difference in means equals zero.

## Details

Test is computed using Maximum Likelihood Estimation. When a gaussian distribution model is used (LOG=FALSE) modeled values may fall below zero, producing unreal p-values (often lower than they should be). Because of this, testing in log units is preferable and is the default.

## References

Helsel, D.R., 2011. Statistics for Censored Environmental Data using Minitab and R, 2nd ed. John Wiley & Sons, USA, N.J.

#' @examples data(PbHeron) cenanova(PbHeron$Liver,PbHeron$LiverCen,PbHeron$DosageGroup) cenanova(PbHeron$Liver,PbHeron$LiverCen,PbHeron$DosageGroup,LOG=FALSE)