Performs a Peto-Peto nonparametric test of differences in cdfs between groups. If more than two groups, the test is followed by a nonparametric multiple comparison test. Uses the BH method of adjusting p-values.

cen1way(x1, x2, group, mcomp.method = "BH", 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. One of the standard methods for adjusting p-values for multiple comparisons. Type ?p.adjust for the list of possible methods. Default is Benjamini-Hochberg "BH" false discover rate. Logical TRUE/FALSE option of whether to print the resulting statistics in the console window, or not. Default is TRUE.

Value

A list of summary statistics for each group evaluated containing the following components:

• N Number of samples

• PctND Percentage of non-detects

• KMmean Kaplan-Meier estimate of the mean

• KMsd Kaplan-Meier estimate of standard deviation

• KMmedian Kaplan-Meier estmate of the median

Peto-Peto test results including Chi-Squared value, degrees of freedom and p-value of the test.

If more than two groups, p-values of the pairwise multiple comparisons, adjusted using the BH false-discovery rate, are reported.

References

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

Peto, R., Peto, J., 1972. Asymptotically Efficient Rank Invariant Test Procedures. Journal of the Royal Statistical Society. Series A (General) 135, 185. doi: 10.2307/2344317

Benjamini, Y., Hochberg, Y., 1995. Controlling the False Discovery Rate: A Practical and Powerful Approach to Multiple Testing. Journal of the Royal Statistical Society. Series B (Methodological), 57, 289-300.

Examples

data(PbHeron)

# Two Groups
cen1way(PbHeron$Liver,PbHeron$LiverCen,PbHeron$DosageGroup) #> Warning: One or more group(s) do not have censored data.#> grp N PctND KMmean KMsd KMmedian #> 1 High 13 0.00 9.2880 16.39000 0.2615 #> 2 Low 14 28.57 0.1202 0.09919 0.09893 #> #> Oneway Peto-Peto test of CensData: PbHeron$Liver   by Factor: PbHeron$DosageGroup #> Chisq = 7.388 on 1 degrees of freedom p = 0.00657 # More than two groups cen1way(PbHeron$Liver,PbHeron$LiverCen,PbHeron$Group)
#> Warning: One or more group(s) do not have censored data.#> Warning: One or more group(s) do not have censored data.#>     grp   N   PctND    KMmean       KMsd   KMmedian
#> 1     1   7   28.57    0.1020    0.08834    0.09893
#> 2     2   7   28.57    0.1384    0.10590     0.1748
#> 3     3   6    0.00   12.1100   16.16000      3.639
#> 4     4   7    0.00    6.8660   17.46000     0.2615
#>
#>       Oneway Peto-Peto test of CensData: PbHeron$Liver by Factor: PbHeron$Group
#>       Chisq = 7.795   on 3 degrees of freedom     p = 0.0504
#>
#> 	Pairwise comparisons using Peto & Peto test
#>
#> data:  CensData and Factor
#>
#>   1     2     3
#> 2 0.887 -     -
#> 3 0.171 0.321 -
#> 4 0.079 0.127 0.887
#>
#> P value adjustment method: BH