The Linear Approach to the Concept of Personality 241Removing differences in elevation and spread prevents one
person from having more traits than another, as well as from
being more extreme. Correcting for elevation is quite defensi-
ble in the special case where the variable set is completely bal-
anced (i.e., consists of opposites like reliable and unreliable).
Except in a fairly poetic manner, it hardly makes sense for a
person to be both moreXand un-Xthan another; it is more
parsimonious to attribute such a response pattern to excentric
scale use, traditionally denoted as the acquiescent response
set. Hofstee et al. (1998; see also Ten Berge, 1999) presented
ways to correct for excentric responding. However, if the vari-
ables set is not balanced, correcting for elevation removes
content and social desirability variance. In the most elemen-
tary case, John is prevented from being both more friendly and
reliable than Mary. That consequence is infelicitous.
The person-centered approach is thus subject to an irony
of fate: An intention (a proper approach to personality) mate-
rializes into an operation (ipsative scoring) that appears to
cradle aversive implications (for the very concept of person-
ality). Ipsatization would do the job in a strictly idiographic
approach, but that condition is not fulfilled: By virtue of the
fact that one and the same method and vocabulary is applied
to more than one person, interindividual comparison auto-
matically creeps in. It may make sense to separate ipsative
and normative components of a scores matrix by representing
the latter as a vector containing the person means. Discarding
that vector, however, has the effect of flattening the concept
of personality. Essentially the same argument applies to indi-
vidual differences in spread (and other moments of the score
distribution).
Dynamics
Analytically, a dynamic approach to personality, as advo-
cated by person-centered investigators, may mean either of
two things: taking the time or growth dimension into account,
and interpreting traits as an intra-individual pattern, there-
fore, in a nonlinear fashion. The dynamic approach thus
stands in opposition to an orthodox trait approach, which is
static and linear.
However, dynamics are easily accommodated in the
individual-differences paradigm. A chronological series of
assessments pertaining to an individual may be conceived as
an extension of the scores vector. In a multiple prediction of
some criterion, the question then becomes whether, for ex-
ample, last year’s emotional stability has incremental validity
over today’s. Alternatively, a (fitted) growth curve may be
represented by its first derivative representing growth speed,
its second derivative representing growth acceleration, and
so on, in addition to the overall score of that individual.
Again, the derivatives function as extra traits. Similarly,
pattern interpretation may be represented by introducing
extra predictors, in this case, moderator or interaction terms
formed by multiplication of predictors. Thoroughbred trait
psychologists would argue that growth and pattern scores
cannot be expected to have incremental validity, but that
is not an objection of principle. What this brief analysis
shows is that the two paradigms are not ideologically incom-
patible but appear to consist of different generalized expecta-
tions regarding the relevance of growth and moderator terms.
A final wording of the moderator issue is whether single
predictors may receive different weights according to the indi-
vidual in question; thus, whether Mary’s emotional stability
may be less relevant in predicting her performance as a pursuit
plane pilot than is John’s. Again, there is no a priori reason
why the weights should be uniform. A technical problem is that
the Pearson correlation is undefined in the single case; how-
ever, raw-score association coefficients like Gower’s (1971)
and Zegers and Ten Berge’s (1985) can do the job. Their appli-
cation to the single case also gives a precise expression to
the otherwise elusive idea of intra-individual trait structure.
The Gower coefficient for the general case is the mean of the
single-case coefficients; it thus writes interindividual structure
as the mean of intra-individual structures, thereby joining two
paradigms of personality that are usually brought in opposition
to each other. This integration is still another reason for taking
raw scores seriously. An empirical problem, however, is that
individual weights may be extremely unstable. However, the
same holds for intra-individual structure.Ranges of ApplicationAfter digesting a number of red herrings, what remains is a
matter of conventional preference. The trait psychologist rep-
resents the person as a vector of scores on a continuous scale,
whereas the typologist would prefer a single qualification on a
binary (applicable vs. not applicable) scale. Taking a sophisti-
cated trait model incorporating growth and moderator effects,
the person-centered approach is a special or degenerate case
of it, and can therefore not be psychometrically superior in
any respect. To justify the type approach, a different perspec-
tive should be adopted. To that end, I distinguish between a
context of prediction and a context of communication.
Given the same basic materials, there can be no reasonable
doubt that the trait approach is superior in a predictive con-
text. On the one hand, typing consists of discarding informa-
tion that is potentially valid. On the other, it introduces
dynamic predictor terms whose empirical status is highly
dubious; therefore, even an orthodox trait approach may be
expected to do better upon cross validation.