Radius of observed planetesimal belts as a function of host star luminosity (black and white points with error bars). The white shaded region represents the ±1σ range of power laws (about the best fit) allowed by the data, including the intrinsic scatter as well as the uncertainty in the observed radii. The background colour map represents the selection probability (%), or percentage of belts that would pass the selection effects at a given [R-L_⋆] location, assuming unobserved belts have the same distribution of parameters [d,R_BB/R, M, λ₀ , β] as the observed population.