${\mu}m$ luminosity, with the result that ${\sim}50$% of galaxies with $L_{60\mu}> 10^{11.2}h^{-2}L_{\odot}$ are strong OH masers ($h = H_o/(100{\rm\, km\,s}^{-1}$). The odds decline to ${\sim}5$% for samples where $L_{60\mu} \approx 10^{9}L_{\odot}$. There is a striking correlation between OH luminosity $L_{OH}$ and $L_{60\mu}$, with $L_{OH} \propto L_{60\mu}^2$ (Baan et al 1992a, Baan 1989, Martin et al 1989).

A picture explaining both the probability of detection and the relative strengths of megamaser emission from objects of different $L_{60\mu}$ has the maser strength depending on strength of the starburst activity in the galaxy (Baan 1989, Henkel et al 1991). Major merger and interaction events are the strongest stimulants of star formation and also produce the most turbulent interstellar gas distributions; these conditions provide the strongest IR fluxes for pumping the maser levels, as well as the largest covering factors of the star forming regions, leading to the greatest probability that views from random directions will see OH maser activity. Galaxies with milder star formation have more placid disks, and maser emission is then observed only by observers who view the galaxies nearly edge-on to their planes. The strong association between the ultra-luminous FIR galaxies and strongly-interacting and merging systems has been recently discussed 