The detection of periodicity in QSO data sets

The issue of periodicity in quasi-stellar object (QSO) data sets is re-examined in the light of the failure to detect a periodicity in the 2dF QSO Redshift Survey, and of a recent claim that edge effects might have generated a spurious periodicity of 0.089 in log10(1 +z) in earlier data sets. A new methodology is described by which the contribution of edge effects may be assessed. It is shown that they have not in fact induced a spurious periodicity in the earlier data sets. Several possible factors are discussed which may tend to mask the periodicity in the 2dF Survey. Thus the earlier evidence for the periodicity in QSO redshifts is unaffected, although new constraints on astrophysical models may be imposed.