Cumulative distributions of the frequency of excesses obtained in this work (black) and those obtained from Spitzer/MIPS results Bryden et al. (2006; cyan), both plotted against fractional dust luminosity. The green straight line is a fit to the values of the frequencies at the less steep part of our cumulative distribution. The extrapolation down to 10^-7, the current estimate of the Kuiper-belt fractional luminosity, gives a prediction for the incidence rate of excesses of ~0.25. The extrapolation from a straight line, plotted in red, fitted to the steeper part of the distribution, that mimics the MIPS results, gives a higher prediction ~0.35. The prediction from the Bryden et al. (2006) distribution, from the blue straight-line fit, is ~0.32. See text for details.