  In recent years there have been many reported detections of highly redshifted
or blueshifted narrow spectral lines (both emission or absorption) in the X-ray
spectra of active galaxies, but these are all modest detections in terms of
their statistical significance. The aim of this paper is to review the issue of
the significance of these detections and, in particular, take account of
publication bias. A literature search revealed 38 reported detections of
narrow, strongly shifted (v/c >= 0.05) X-ray lines in the 1.5-20 keV spectra of
Seyfert galaxies and quasars. These published data show a close, linear
relationship between the estimated line strength and its uncertainty, in the
sense that better observations (with smaller uncertainties) only ever show the
smallest lines. This result is consistent with many of the reported lines being
false detections resulting from random fluctuations, drawn from a large body of
data and filtered by publication bias such that only the most `significant'
fluctuations are ever reported. The reality of many of these features, and
certainly their prevalence in the population at large, therefore remains an
open question that is best settled though uniform analysis (and reporting) of
higher quality observations.
