Histograms of the significance of on-pulses and off-pulses for the 20 pulsars. Normal functions with mean zero and standard derivation σ_off are employed to model the distribution of off-pulse significance, scaled with f_n and represented by a red dotted line. The residual distribution of on-pulse significance is plotted below and modeled by lognormal functions with mean μ_on and standard derivation σ_on.