[en] The luminosity dependence of the equivalent width of CIV in active galaxies, the Baldwin effect, is shown to be a consequence of a luminosity dependent ionization parameter. This law also agrees with the lack of a Baldwin effect in Ly alpha or other hydrogen lines. A fit to the available data gives a weak indication that the mean covering factor decreases with increasing luminosity, consistent with the inference from X-ray observations. The effects of continuum shape and density on various line ratios of interest are discussed