### How close is a complex movement model to reality?

```How close is a complex movement
model to reality?
Jonathan Potts, Marie Auger-Méthé,
Karl Morkoss, Mark Lewis
Some history
Some history
One outcome:
• Often conclusions are made based on relative
fit between models
One outcome:
• Often conclusions are made based on relative
fit between models
• Suggestion: look at the residuals in step-length
and turning angle distributions
How do we extend the idea of a
residual to more complex movement
models?
Generic movement kernel: probability of moving to x
at a time τ in the future given that the agent is
currently at y and arrived there on a bearing θ and is
travelling through environment E is  (|, , )
How do we extend the idea of a
residual to more complex movement
models?
Generic movement kernel: probability of moving to x
at a time τ in the future given that the agent is
currently at y and arrived there on a bearing θ and is
travelling through environment E is  (|, , )
Study species
e.g. topography
e.g. food
distribution
Actual move
Earth mover`s distance: a generalised
residual
Earth mover`s distance: a generalised
residual
()
Ω
, ,  | − 0 |

•  is the actual place the animal moves to
Standardised earth mover`s distance
Ω
,  | − 0 |

2
,    −
=
Ω
,
Ω
How close is your model to the data?
Test the following null hypothesis:
H0: “The data is indistinguishable from a
stochastic realisation of the model”
Power test on simulated data
Researcher
layer 1
C(x)
T(x)
Researcher
doesn’t know
Power test on simulated data
Researcher
layer 1
C(x)
Researcher
doesn’t know
T(x)
“Real” process:    ∝ − − +
−()
Best model:    ∝ − − +

Power test on simulated data
Potts JR, Auger-Méthé M, Mokross K, Lewis MA. A generalized residual technique for analyzing complex movement models using
earth mover's distance. Methods Ecol Evol DOI: 10.1111/2041-210X.12253
Where is my model failing?
Patterns in EMD
Acknowledgements
Mark Lewis (Alberta)
Marie Auger-Méthé (Dalhousie)
Karl Mokross (Louisiana State)
Conclusion
• Want to know how good your model is in an
absolute rather than relative sense?
Conclusion
• Want to know how good your model is in an
absolute rather than relative sense?
• Use EMD for the best results.
```