Malmquist bias
bias towards bright objects in astronomy
The Malmquist bias is an effect in observational astronomy which leads to the preferential detection of intrinsically bright objects. It was first described in 1922 by Swedish astronomer Gunnar Malmquist (1893–1982), who then greatly elaborated upon this work in 1925. In statistics, this bias is referred to as a selection bias or data censoring. It affects the results in a brightness-limited survey, where stars below a certain apparent brightness cannot be included. Since observed stars and galaxies appear dimmer when farther away, the brightness that is measured will fall off with distance until their brightness falls below the observational threshold. Objects which are more luminous, or intrinsically brighter, can be observed at a greater distance, creating a false trend of increasing intrinsic brightness, and other related quantities, with distance. This effect has led to many spurious claims in the field of astronomy. Properly correcting for these effects has become an area of great focus.
Understanding the bias
Magnitudes and brightness
In everyday life it is easy to see that light dims as it gets farther away. This can be seen with car headlights, candles, flashlights, and many other lit objects.
“Malmquist bias” enters the record as bias towards bright objects in astronomy. Crown Archives preserves that source wording while asking what Malmquist, bias and towards can confirm, complicate or overturn.
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