Individual Differences and Differential
A brief history and
prospect Used by permission of the author. [For classroom use only] William
Revelle Joshua Wilt David M.Condon Northwestern
University Differential psychology has been a central concern to
philosophers and psychologists, both applied and theoretical, for the past
several millennia. It remains so today. he proper study of individual differences
integrates methodology, affective and cognitive science, genetics and biology.
It is a field with a long history and an exciting future. We review some of the
major questions that have been addressed and make suggestions as to future
directions. This handbook is devoted to the study of individual differences and
differential psychology. To write a chapter giving an overview of the field is
challenging, for the study of individual differences includes the study of
affect, behavior, cognition, and motivation as they are affected by biological
causes and environmental events. That is, it includes all of psychology. But it
is also the study of individual differences that are not normally taught in
psychology departments. Human factors, differences in physical abilities as
diverse as taste, smell, or strength are also part of the study of differential
psychology. Differential psychology requires a general knowledge of all of
psychology for people (as well as chimpanzees, dogs, rats and fishes) differ in
many ways. Thus, differential psychologists do not say that they are cognitive
psychologists,
social-psychologists,
neuro-psychologists,
behavior geneticists,
psychometricians, or methodologists, for although we do those various
hyphenated parts of psychology, by saying we study differential psychology, we
have said we do all of those things. And that is true for everyone reading this
handbook. We study differential psychology. Individual differences in how we
think, individual differences in how we feel, individual differences in what we
want and what we need, individual differences in what we do. We study how
people differ and we also study why people differ. We study individual
differences. There has been a long recognized division in psychology between
differential psychologists and experimental psychologists (Cronbach, 1957; H.
J. Eysenck, 1966), however, the past 30 years has seen progress in integration
of these two approaches (Cronbach, 1975; H. J. Eysenck, 1997; Revelle &
Oehleberg, 2008). Indeed, one of the best known experimental psychologists of
the 60’s and 70’s argued that “individual differences ought to be considered
central in theory construction, not peripheral” (Underwood, 1975, p 129).
However, Underwood (1975) went on to argue (p 134) that these individual
differences are not the normal variables of age, sex, IQ or social status, but
rather are the process variables that are essential to our theories. Including
these process variables remains a challenge to differential psychology.
OVERVIEW OF DIFFERENTIAL PSYCHOLOGY The principles of differential psychology
are seen outside psychology in computer science simulations and games, in
medical assessments of disease symptymatology, in college and university
admissions, in high school and career counseling centers, as well as in applied
decision making. Early Differential Psychology and its application Differential
psychology is not new for an un- derstanding of research methodology and
individ- ual differences in ability and affect was described as early as the
Hebrew Bible in the story of Gideon (Judges 6, 7). Gideon was something of a
skeptic who had impressive methodological sophistication. In perhaps the first
published example of a repeated measures, cross over design, he applied several
behavioural tests to God before agreeing to go off to fight the Medians as
instructed. Gideon put a wool fleece out on his threshing floor and first asked
that by the next morning just the fleece should be wet with dew but the floor
should be left dry. Then, the next morning, after this happened, as a cross
over control, he asked for the fleece to be dry and the floor wet. Observing
this double dissociation, Gideon decided to follow God’s commands. We believe
that this is the first published example of the convincing power of a cross
over interaction. (Figure 1 has been reconstructed from the published data.) In
addition to being an early methodologist, Gideon also pioneered the use of a
sequential assessment battery. Leading a troop of 32,000 men to attack the
Midians, Gideon was instructed to reduce the set to a more manageable number
(for greater effect upon achieving victory). To select 300 men from 32,000,
Gideon (again under instructions from God) used a two part test. One part
measured motivation and affect by selecting those 10,000 who were not afraid.
The other measured crystallized intelligence, or at least battlefield
experience, by selecting those 300 who did not lie down to drink water but
rather lapped it with their hands (McPherson, 1901). REVELLE, CONDON,
Gideon thus combined many of the skills of a differential
psychologist.
He was a
methodologist skilled in within subject designs, a student of affect and
behavior as well as familiar with basic principles of assessment. Other early
applications of psy- chological principles to warfare did not emphasize
individual differences so much as the benefits of training troops of a phalanx
(Thucydides, as cited by Driskell & Olmstead, 1989). Early Differential Psychology and its Differential psychology is not new for an
un- distending of research methodology and individual differences in ability
and affect was described as early as the Hebrew Bible in the story of Gideon
(Judges 6, 7). Gideon was something of a skeptic who had impressive
methodological sophistication. In perhaps the first published example of a
repeated measures, cross over design, he applied several be- hairball tests to
God before agreeing to go off to fight the Medians as instructed. Gideon put a
wool fleece out on his threshing floor and first asked that by the next morning
just the fleece should be wet with dew but the floor should be left dry. Then,
the next morning, after this happened, as a cross over control, he asked for
the fleece to be dry and the floor wet. Observing this double dissociation,
Gideon decided to follow God’s commands. We believe that this is the first
published example of the convincing power of a cross over interaction. (Figure
1 has been reconstructed from the published data.) In addition to being an early methodologist,
Gideon also pioneered the use of a sequential as- assessment battery. Leading a
troop of 32,000 men to attack the Midians, Gideon was instructed to reduce the
set to a more manageable number (for greater effect upon achieving victory). To
select 300 men COURSE
GUIDE: Educational Psychology Floor Wool Moistur e 0. 0 0. 2 0. 4 0. 6 0. 8 1. 0 2
Night Figure 1. Gideon’s tests for God are an early example of a double
dissociation and probably the first published example of a cross over
interaction. On the first night, the wool was wet with dew but the floor was
dry. On the second night, the floor was wet but the wool was dry (Judges 6:36-40)
Figure 1. Gideon’s tests for God are an early example of a double
dissociation and probably the first published example of a cross over
interaction. On the first night, the wool was wet with dew but the floor was
dry. On the sec- ond night, the floor was wet but the wool was dry (Judges
REVELLE,
CONDON, WILT Personality taxonomies That people differ is
obvious.
How and why they differ is the subject of taxonomies of
personality and other individual differences. An early and continuing
application of these taxonomies is most clearly seen in the study of leadership
effectiveness. Plato’s discussion of the personality and ability
characteristics required for a philosopher king emphasized the multivariate
problem of the rare cooccurence of appropriate
traits: ... quick intelligence, memory, sagacity, cleverness, and
similar qualities, do not often grow together, and that persons who possess
them and are at the same time high-spirited and magnanimous are not so
constituted by nature as to live orderly and in a peaceful and settled manner;
they are driven any way by their impulses, and all solid principle goes out of
them. ... On the other hand, those
steadfast natures which can better be depended upon, which in a battle are
impregnable to fear and immovable, are equally immovable when there is anything
to be learned; they are always in a torpid state, and are apt to yawn and go to
sleep over any intellectual toil. ... And yet we were saying that both
qualities were necessary in those to whom the higher education is to be
imparted, and who are to share in any office or command. (Plato, 1991, book 6)
Similar work is now done by Robert Hogan and his colleagues as they study the
determinants of leadership effectiveness in management settings (Hogan, 2007,
1994; Hogan et al., 1990; Padilla et al., 2007) as well as one of the editors
of this volume, Adrian Furnham (Furnham, 2005). The dark side qualities
discussed by Hogan could have been taken directly from The Republic. A
typological rather than dimensional model of individual differences was
developed by Theophrastus, a student of Aristotle, who was most famous as a botanical
taxonomist. However, he is known to differential psychologists as a personality
taxonomist who organized the individual differences he observed into a
descriptive taxonomy of “characters”. The characters of Theophrastus are often
used to summarize the lack of coherence of early personality trait description,
although it is possible to organize his “characters” into a table that looks
remarkably similar to equivalent tables of the late 20th century (John, 1990;
John & Srivastava, 1999). 1600 years after Theophrastus, Chaucer added to
the the use of character descriptions in his “Cantebury Tales” which are
certainly the first and probably the “best sequence of ‘Characters’ in English
Literature” (Morley, 1891, pg 2). This tradition continued into the 17th
century where the character writings of the period are fascinating
demonstration of the broad appeal of personality description and
categorization (Morley, 1891).
OVERVIEW OF DIFFERENTIAL PSYCHOLOGY Causal theories
Tyrtamus of Lesbos, who was known as Theophrastus for his speaking ability,
(Morley, 1891), asked a fundamental question of personality theory that is
still of central concern to us today: Often before now have I applied my
thoughts to the puzzling question – one, probably, which will puzzle me for
ever – why it is that, while all Greece lies under the same sky and all the
Greeks are educated alike, it has befallen us to have characters so variously
constituted. This is, of course, the fundamental question asked today by
differential psychologists who study behavior genetics (e.g., Bouchard, 1994,
2004) when they address the relative contribution of genes and shared family
environment as causes of behavior. Biological personality models have also been
with us for more than two millenia, with the work of Plato, Hippocrates and
later Galen having a strong influence. Plato’s organization of the tripartite
soul into the head, the heart and the liver (or, alterna- tively, reason,
emotion and desire) remains the classic organization of the study of individual
differences (Hilgard, 1980; Mayer, 2001; Revelle, 2007). Indeed, with the
addition of behavior, the study of psychology may be said to be the study of
affect (emotion), behavior, cognition (reason) and motivation (desire) as
organized by Plato (but without the
physical localization!). 500
years later, the great doctor, pharmacologist and physiologist, Galen (129-c.a.
216) organized and extended the earlier literature of his time, particularly
the work of Plato and Hippocrates (c 450-380 BCE), when he described the causal
basis of the four temperaments. His empirical work, based upon comparative
neuroanatomy, provided support for Plato’s tripartite organization of affect,
cognition, and desire. Although current work does not use the same biological
concepts, the search for a biological basis of individual differences continues
to this day. 1800 years later, Wilhelm Wundt (Wundt, 1874,1904) reorganized the
Hippocrates/ Galen four temperaments into the two dimensional model later
discussed by Hans Eysenck (H. J. Eysenck, 1965, 1967) and Jan Strelau (Strelau,
1998).
