Highlighting the Patterns in Missing Values in Trajects
runsNAltraj performs a runs test to detect any autocorrelation
in the location of missing relocations, for each burst of an object of
class ltraj.
summaryNAltraj returns a summary of the number and proportion
of missing values for each burst of an object of class
ltraj.
plotNAltraj plots the missing values in an object of class
ltraj against the time.
runsNAltraj(x, nrep = 500, plotit = TRUE, ...) summaryNAltraj(x) plotNAltraj(x, ...)
x |
An object of class |
nrep |
Number of randomisations |
plotit |
logical. Whether the results should be plotted on a graph |
... |
Further arguments to be passed to the generic function
|
The statistics used here for the test is the number of runs in the sequence of relocations. For example, the sequence reloc-NA-NA-reloc-reloc-reloc-NA-NA-NA-reloc contains 5 runs, 3 runs of successful relocations and 2 runs of missing values. Under the hypothesis of random distribution of the missing values in the sequence, the theoretical expectation and standard deviation of the number of runs is known. The runs test is a randomization test that compares the standardized value of the number of runs (i.e. (value-expectation)/(standard deviation)) to the distribution of values obtained after randomizing the distribution of the NA in the sequence. Thus, a negative value of this standardized number of runs indicates that the missing values tend to be clustered together in the sequence.
runsNAltraj returns a list of objects of class
randtest (if a burst does not contain any missing value, the
corresponding component is NULL).
In the versions of adehabitatLT prior to 0.3.21, a bug occurred in the calculation of the P-value (the test actually presented the value 1-P). This bug is now corrected.
Clement Calenge clement.calenge@ofb.gouv.fr
## Two relocations are theoretically separated by ## 10 minutes (600 seconds) data(puechcirc) puechcirc ## plot the missing values plotNAltraj(puechcirc) ## Test for an autocorrelation pattern in the missing values (runsNAltraj(puechcirc))
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