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Published online by Cambridge University Press: 12 April 2016
We performed a new analysis of the В and R light curves of a sample of PG QSOs. We confirm a variability-redshift correlation and its interpretation in terms of spectral variability. We find an intra-QSO and an inter-QSO α;-L correlation. The former can be explained neither by presence of the host galaxy nor by changes of the accretion rate. Hot spots due to accretion disk instabilities could explain the observations.