Observed distribution vs. selection bias. The green curves denote the median and 90% credible bounds for the distribution of V_GW on the analyzed O1–O4a events shown in Figure 5. The blue dashed line and solid contours denote the median estimate for the marginalized detection probability or sensitive volume V_sens(V_GW), together with the 90% credible bounds. The dotted contour represents the 90% credible bounds on the median.