Periodicity versus selection effects in the redshift distribution of QSOs

Periodicities and selection effects in the redshift (z) distribution of QSO s have been debated for a long time in the literature. Here we show that pe aks and troughs in the redshift distribution of three new samples, claimed to demonstrate the existence of a periodicity, can be interpreted in terms of known selection effects. This analysis confirms earlier findings that th e presence of such selection effects seriously weakens any suggestion for p eriodicity of the form Delta ln(1 + z) = constant.