Editing Francis Galton (section)

===Regression toward the mean===
Galton was the first to describe and explain the common phenomenon of [[regression toward the mean]], which he first observed in his experiments on the size of the seeds of successive generations of sweet peas.

The conditions under which regression toward the mean occurs depend on the way the term is mathematically defined. Galton first observed the phenomenon in the context of [[simple linear regression]] of data points. Galton{{sfn|Galton|1889|p=}} developed the following model: pellets fall through a ''[[quincunx]]'' or "[[bean machine]]" forming a normal distribution centred directly under their entrance point. These pellets could then be released down into a second gallery (corresponding to a second measurement occasion). Galton then asked the reverse question "from where did these pellets come?"
{{blockquote|The answer was not "on average directly above". Rather it was "on average, more towards the middle", for the simple reason that there were more pellets above it towards the middle that could wander left than there were in the left extreme that could wander to the right, inwards.|source={{harvnb|Stigler|2010|p=477}}}}