Quality & Quantity (2006) 40:407–418 © Springer 2006
The Bell Curve in Psychological Research
and Practice: Myth or Reality?
Centro Docimologico, Department of Psychology and Cultural Anthropology, University of
Verona, Italy. E-mails: firstname.lastname@example.org; email@example.com
Abstract. The expression “the bell curve” designs both a kind of statistical distribution and
the title of a famous and controversial book by Herrnstein and Murray. The ﬁrst is so
attractive that the second refers to it to give more credibility to its questionable theories on
intelligence. The point is that, during the 20th century, the bell curve has assumed a more
and more important role in psychological research and practice and have become both a
reality and a myth. In the ﬁrst case (reality) we can assist to appropriate applications of a
real useful statistical concept. In the second (myth) we can have two kinds of attitudes: one
attitude is typical of those researchers who search for normality in all their data and vari-
ables, just as Parsifal used to search for the Holy Graal (we call this “the Parsifal attitude”);
the other is typical of those researchers who give normality for granted and act as if it were
a Platonic Idea (we call this “the Plato attitude”). The article discusses the role of the nor-
mal distribution in psychological research and practice and shows how it can be dangerous
to treat the bell curve as a God or an Idol.
Key words: normal distribution, psychological measurement and testing, intelligence and IQ
I know of scarcely anything so apt to impress the imagination as the
wonderful form of cosmic order expressed by the “Law of Frequency
of Error”. The law would have been personiﬁed by the Greeks and dei-
ﬁed, if they had known of it. It reigns with serenity and in complete
self-effacement amidst the wildest confusion.
Sir Francis Galton, Natural Inheritance, 1889
The Gaussian error law came to act as a veritable Procrustean bed
to which all possible measurements should be made to ﬁt. The belief
in authority so typical of modern German learning and which has also
spread to America was too great to question the supposed generality of
the law discovered by the great Gauss.
Sir Ronald Aylmer Fisher, The mathematical Theory of Probability,