Regression to the Mean
by Andrew Porter
If something varies normally between two far extremes,
It usually swings back naturally to values in between.
From sport to crime and illnesses, we see this common theme,
An effect we call, statistically, 'regression to the mean'.
When Brucie plays his cards right and he's holding up a queen,
You know that next a lower card is likely to be seen,
Because there are so many cards much lower than a queen.
It's simple probability, it's 'regression to the mean'.
Random fluctuations of performances in sports,
Befuddle sports professionals, who use gimmicks of all sorts,
Crystals, magnets, copper bracelets they esteem,
But improvements in achievement are 'regression to the mean'.
A man with awful backache, that sometimes gets much worse,
May turn to herbal remedies and swear his pain's reversed.
Perhaps it has, but not because the herbalist intervened,
The pain will ease quite simply through 'regression to the mean'.
Evidence-based treatments that doctors should assign,
Use tests that will be randomized, controlled and double-blind,
Stopping self-deception before those test-results are seen,
It stops them being fooled by 'regression to the mean'.