This is incidentally another way of explaining the effect. Consider the standard diagram of the joint probability density and how it relates to correlation. Now take a bite out of the upper right corner of big X and big Y events: unless the joint density started in a really strange shape this will tend to make the correlation negative.
This is known as Berkson’s paradox and it is ubiquitous. A lot of people have written about it and its implications, e.g. Yvain (underlying reasons why anti-correlations arise are very similar).
Similar in that one quadrant is empty, otherwise a distinct effect.
This is incidentally another way of explaining the effect. Consider the standard diagram of the joint probability density and how it relates to correlation. Now take a bite out of the upper right corner of big X and big Y events: unless the joint density started in a really strange shape this will tend to make the correlation negative.
This is known as Berkson’s paradox and it is ubiquitous. A lot of people have written about it and its implications, e.g. Yvain (underlying reasons why anti-correlations arise are very similar).