Annu. Rev. Astron. Astrophys. 1997. 35: 101-136
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2.3. The Scott Effect

Scott (1957) published an important paper on "The Brightest Galaxy in a Cluster as a Distance Indicator." Looking back to this study, one may find it contained many basic points that were later discussed in connection with the Malmquist bias of the second kind. Her concern was how the availability of a distant cluster of galaxies influences the use of its brightest galaxy as a standard candle. Availability means that (a) at least n cluster members must be brighter than the limiting magnitude m1 of the plate, and (b) the apparent magnitude of the brightest galaxy must be brighter than another limit m2, which is needed for measurements of magnitude and redshift. Let us pick up a few conclusions of Scott (1957, p. 249):

Scott used both numerical simulations and an analytical model to show the size of systematic errors that the condition of availability causes to the derived distance at different true distances, and she concluded that the selection effect is bound to influence seriously the Hubble m-z diagram constructed for brightest cluster galaxies. She (1957, p. 264) also concluded that

She (1957, p. 264) also pondered about how to make a difference between a real and selection-induced deviation from linearity in the Hubble law:

Of the above two extracts, Hubble's application is clearly concerned with the classical Malmquist bias (or Kapteyn's Problem II), whereas the discussion by Scott has a relation to Kapteyn's Problem I, though the effect in galaxy clusters is more complicated. In fact, there is no mention of the classical Malmquist bias in Scott's paper and really no need for it.

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