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#In 1989, Martin R. Croasdale reported finding a quantization of redshifts using a different sample of galaxies in increments of 72 km/s or Δ''z'' = {{val|2.4|e=-4}} (where Δ''z'' denotes shift in frequency expressed as a proportion of initial frequency).<ref>{{cite journal |bibcode=1989ApJ...345...72C|doi = 10.1086/167882 | title=Periodicities in galaxy redshifts | journal=The Astrophysical Journal |date=1989 |volume=345 |pages=72 |first=Martin R. |last=Croasdale}}</ref>
#In 1990, Bruce Guthrie and William Napier reported finding a "possible periodicity" of the same magnitude for a slightly larger data set limited to bright [[spiral galaxy|spiral galaxies]] and excluding other types.<ref>{{cite journal |bibcode=1990MNRAS.243..431G|doi = | title=The Virgo cluster as a test for quantization of extragalactic redshifts | journal=Monthly Notices of the Royal Astronomical Society |date=1990 |volume=243 |pages=431–442 |first1=B. N. G.|last1=Guthrie|first2=W. M.|last2=Napier}}</ref>
#In 1992, Guthrie and Napier proposed the observation of a different periodicity in increments of Δ''z'' = {{val|1.24|e=-4}} in a sample of 89 galaxies.<ref>{{cite journal |bibcode=1991MNRAS.253..533G|doi = 10.1093/mnras/253.3.533| title=Evidence for redshift periodicity in nearby field galaxies | journal=Monthly Notices of the Royal Astronomical Society |date=1991 |volume=253 |issue = 3|pages=533–544 |first1=B. N. G.|last1=Guthrie|first2=W. M.|last2=Napier|doi-access=free}}</ref>
#In 1992, Paal ''et al.'' and Holba ''et al.'' concluded that there was an unexplained periodicity of redshifts in a reanalysis of a large sample of galaxies.<ref>{{cite journal|bibcode=1992Ap&SS.191..107P|doi = 10.1007/BF00644200 | title=Inflation and compactification from Galaxy redshifts? | journal=Astrophysics and Space Science|date=1992|volume=191|issue=1|pages=107–124|first=G.|last=Paal}}</ref><ref>{{cite journal |bibcode=1992Ap&SS.198..111H|doi = 10.1007/BF00644305 | title=Cosmological parameters and redshift periodicity | journal=Astrophysics and Space Science |date=1992 |volume=198 |issue=1 |pages=111–120 |first=Ágnes |last=Holba}} See also reference to {{cite journal|bibcode=1990Natur.343..726B|doi = 10.1038/343726a0 | volume=343 | issue=6260|title=Large-scale distribution of galaxies at the Galactic poles|journal=Nature|date=1990|pages=726–728|first=T. J.|last=Broadhurst}}</ref>
#In 1997, Guthrie and Napier concluded the same:
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:"Given that there are almost eight times as many data points in this sample as in the previous analysis by Burbidge & Napier (2001), we must conclude that the previous detection of a periodic signal arose from the combination of noise and the effects of the window function."<ref>{{cite journal|author1=Hawkins|author2=Maddox|author3=Merrifield|title=No Periodicities in 2dF Redshift Survey Data|doi=10.1046/j.1365-8711.2002.05940.x|date=2002|journal=Monthly Notices of the Royal Astronomical Society|volume=336|pages=L13–L16|issue=13|arxiv=astro-ph/0208117|bibcode = 2002MNRAS.336L..13H }}</ref>
In response, Napier and Burbidge (2003) argue that the methods employed by Hawkins ''et al.'' to remove noise from their samples amount to "excessive data smoothing" which could hide a true periodicity. They publish an alternate methodology for this that preserves the periodicity observed in earlier studies.<ref>{{cite journal|last1=Napier|first1=W. M.|last2=Burbidge|first2=G. R.|title=The detection of periodicity in QSO data sets|date=2003|journal=Monthly Notices of the Royal Astronomical Society|volume=342|pages=601–604|issue= 2|doi=10.1046/j.1365-8711.2003.06567.x |bibcode = 2003MNRAS.342..601N |doi-access=free}}</ref>
In 2005, Tang and Zhang found no evidence for redshift quantization of quasars in samples from the [[Sloan Digital Sky Survey]] and 2dF redshift survey.<ref name="Tang"/>
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