Authors: Michael Pürrer¹, P. Ajith^2,3, Mark Hannam¹, Sascha Husa^4
1School of Physics and Astronomy, Cardiff University, Queens Building, CF24 3AA, Cardiff, United Kingdom
²LIGO Laboratory, California Institute of Technology, Pasadena, CA 91125, USA
³Theoretical Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
⁴Departament de Fisica, Universitat de les Illes Balears, Crta. Valldemossa km 7.5, E-07122 Palma, Spain

An effective spin parameter allows us to capture the dominant spin effects in compact binary coalescences, while reducing the number of physical parameters in a waveform model. An effective-spin PN inspiral model has been shown to be both effectual and faithful, and a similar parameter has also been used in recent phenomenological inspiral-merger-ringdown (IMR) models for black-hole binaries. While the use of such an approximation is well motivated by post-Newtonian theory, its validity has not yet been tested on full IMR waveforms. We present the results of a study aimed at quantifying that validity.