The function Cs
computes the coefficient of sociality between two moving
objects following the methods outlined by Kenward et al. (1993). It also uses a
signed Wilcoxonrank test to test for significance.
1  Cs(traj1, traj2, tc = 0)

traj1 
an object of the class 
traj2 
same as 
tc 
time threshold for determining simultaneous fixes – see function: 
This function can be used to calculate the Kenward et al. (1993) coefficient of sociality (Cs) between two animals. The Cs statistic tests the observed mean distance between simultaneous fixes against that expected by the overall distribution of distances between all fixes.
Cs=(DeDo)/(De+Do)
Where Do is the mean observed distance between simultaneous fixes, and De
is the mean expected distance between all fixes. Kenward et al. (1993) propose Cs
as a useful metric for exploring attraction or avoidance behaviour.
Values for Cs closer to 1 indicate
attraction, while values for Cs closer to 1 indicate avoidance. Values of Cs
near 0 indicate that the two animals' movements have no influence on one another.
Further, the difference between the observed and expected distances are compared
using a paired signedrank test (both onesided tests, indicative of attraction
or avoidance). See the function GetSimultaneous
for details on how
simultaneous fixes are determined from two trajectories.
This function returns a list of objects representing the calculated values from the Cs statistic and associated pvalues from the signed rank test.
Do – The mean distance of simultaneous fixes.
De – The mean expected distance, from all fixes.
Cs – The coefficient of sociality, see Details.
p.Attract – One sided pvalue from signed rank test, testing for attraction.
p.Avoid – One sided pvalue from signed rank test, testing for avoidance.
Kenward, R.E., Marcstrom, V. and Karlbom, M. (1993) Postnestling behaviour in goshawks, Accipiter gentilis: II. Sex differences in sociality and nestswitching. Animal Behaviour. 46, 371–378.
GetSimultaneous
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