Time-delayed response of the broad Hα line as as a function of Hα luminosity. Since the response time is directly related to the BLR radius by R = cτ, this is known as the R–L relationship. Blue circles are from the RM database (Table A.1) and green triangles are from SDSS-RM (Table B.1). The solid line shows the best fit to Eq. (2), with parameters given in the second line of Table 1. The short- and long-dashed line show the ±1σ and ±2.6σ envelopes, respectively.