Where does alpha collide?

Berger's 1929 Über das Elektrenkephalogramm des Menschen recorded the first human electroencephalogram and named the alpha rhythm: the prominent brain wave near ten cycles per second that appears when a person is awake but relaxed with the eyes closed, and that fades when the eyes open or attention sharpens. The referent is an oscillation of electrical activity measured at the scalp, described by its frequency and its amplitude. It is a pattern produced by living brain tissue, and it has nothing in common with a coefficient computed from test scores or a number describing an investment's return beyond the shared Greek letter.[1]

Unit

One oscillation of scalp voltage in the eight to thirteen hertz band

Recovery means

Not applicable

Measured by

Recorded by electroencephalography and quantified as the power in the alpha frequency band

Cronbach's 1951 Coefficient alpha and the internal structure of tests named coefficient alpha: a number, usually between zero and one, that estimates how consistently the items of a test measure the same underlying thing, generalising an earlier Kuder-Richardson formula. A high value means the items tend to move together across the people who answer them, so the total score is a stable summary. The referent is a property of a set of measurements, computed from the correlations among items, and it is unrelated to a rhythm recorded from the brain or to the return earned by a fund.[2]

Unit

A dimensionless coefficient, typically scaled from zero to one

Recovery means

Not applicable

Measured by

Computed from the number of items and the average correlation among the items of a scale

Jensen's 1968 The performance of mutual funds in the period 1945-1964 defined alpha: the part of a portfolio's return that exceeds what its exposure to market risk would predict, estimated as the intercept in a regression of the portfolio's excess return on the market's excess return. A positive alpha is read as evidence that a manager added value beyond simply bearing market risk. The referent is a measured performance gap for an investment, expressed as a rate of return, and it bears no relation to a rhythm in the brain or to the internal consistency of a test.[3]

Unit

A rate of return above the benchmark, in percent per period

Recovery means

Not applicable

Measured by

Estimated as the intercept of a regression of excess portfolio return on excess market return