Evolution of the observed “starburst” fraction with redshift, where starbursts galaxies are defined as having an SFR enhanced by at least a factor X_SB compared to the SFR on the main sequence. Our results are shown for X_SB = 4, 3 and 2.5 as diamonds (black, gray, and white, respectively), slightly offset in redshift for clarity. Only points where the starburst sample is complete are shown, and error bars are estimated using bootstrapping. We also show the value observed by Rodighiero et al. (2011) at z = 2 as a filled red star, which was obtained with X_SB = 4. These figures are compared qualitatively to the observed pair fraction reported by Kartaltepe et al. (2007) as open blue triangles, and the range of major merger fractions predicted by Hopkins et al. (2010a) is shown with dashed purple lines. It is clear that, both in observations and simulations, the merger fraction evolves significantly faster than the observed starburst fraction, the latter remaining almost constant regardless of the precise definition of what is a “starburst”.