# mannkendall: Mann-kendall test for trend In emon: Tools for Environmental and Ecological Survey Design

## Description

Calculates the Mann-Kendall statistic for monotonic trend and also the p-value against the null hypothesis of no trend. Unlike the function `MannKendall`, works for repeat values of time.

## Usage

 `1` ``` mannkendall(time, Y, nsims.mk=999) ```

## Arguments

 `time` Vector of values which define the direction of the trend. `Y` Vector of values for which you want to determine the trend. `nsims.mk` Number of replicate permuations to calculate the p-value. Default=999.

## Details

Error checks of parameters not included so as not to slow down mannkendall. The statistic is calculated by considering each case `j` and considering the subset of observations that have time greater than `time[j]`. The Mann Kendall statistic is the number of observations in this subset for which `Y > Y[j]` minus the number for which `Y < Y[j]`. The statistic is summed over all `j`. The p-value is calculated by `nreps` random permutations of the Y values.

## Value

 `mann` Mann-Kendall statistic of observed data, as calculated by `mannkendall.stat`. `pvalue` P-value assuming a null hypothesis of no trend and two-way alternative hypothesis.

## Author(s)

Jon Barry: [email protected]

## References

Mann, H.B. (1945), Nonparametric tests against trend, Econometrica, 13, 245-259.

Kendall, M.G. 1975. Rank Correlation Methods, 4th edition, Charles Griffin, London.

`mannkendall.stat`, `power.trend`, `MannKendall`
 ```1 2 3``` ```x = rep(1:10,rep(2,10)) y = rnorm(20, 5, 2) mannkendall(x, y) ```