Optical variability and redshift of QSOs

It is found from reviewing homogeneous sets of data on the optical variability of QSOs that there is a remarkable dependency of the degree of variability on redshift. The redshift distribution of the three classes into which QSOs have been divided on the basis of their degree of variability is presented. Attention is given to the fact that while the nonvariable objects are spread out more or less uniformly on the redshift scale, there is a clear tendency for the optically violent variable objects to be located on the lower redshift range. It is noted that the probability of finding QSOs with a greater degree of variability is larger for objects with lower redshifts and that objects with redshifts smaller than 1.0 are more likely candidates for violent variables