Subsequent discourse focused upon whether redshift surveys of quasars (QSOs) have produced evidence of quantization in excess of what is expected due to selection effect or galactic clustering.
[27] A 2001 study by Burbidge and Napier found the pattern of periodicity predicted by Karlsson's formula to be present at a high confidence level in three new samples of quasars, concluding that their findings are inexplicable by spectroscopic or similar selection effects.
[32][33] Bell and Comeau (2010) concur that selection effects give rise to the apparent redshift peaks, but argue that the correction process removes a large fraction of the data.
The authors argue that the "filter gap footprint" renders it impossible to verify or falsify the presence of a true redshift peak at Δz = 0.60.
[34] A 2006 review by Bajan et al. discovered weak effects of redshift periodization in data from the Local Group of galaxies and the Hercules Supercluster.