Clinical Judgments of General Intelligence
in Relation to Obtained IQ

Thurber S, Lee R, Bonynge E


Licensed clinicians representing psychiatry, clinical psychology, social work, nursing, and marriage and family counseling, estimated the general intellectual functioning of  adult patients as part of an initial assessment. Several hundred of these estimates were made across a four year period. These estimates were compared to tests of general intelligence administered subsequently to 78 of these patients. Contrary to data suggesting prototypically inaccurate clinical judgments, these clinicians evinced reasonably precise predictions.


In the middle of the last century, Paul Meehl authored a seminal text on  the accuracy of clinical versus statistical prediction (Meehl, 1954) in which he summarized research data suggesting the human brain is no match to predictions based on measurement and statistical weighting of predictor variables. Subsequently, Meehl and his colleagues have repeatedly affirmed the general superiority of actuarial predictions over clinical judgments while acknowledging that the two methods should complement each other as approaches for predictive decision-making. Nevertheless, he averred that there were still only a paucity of studies supporting a weak proclivity favoring clinical judgment compared to the preponderance of researches corroborating the superiority of actuarial prognostications of such criteria as future criminal behavior and educational achievement (see Meehl, 1986; Meehl, 1997; Dawes, Faust, & Meehl, 1989).


Several investigations have focused on the problems in information processing by mental health clinicians that may impede accurate clinical predictions. In combining multiple sources of information about patients, for example, clinicians may use impressionistic weighting procedures that are far from optimal (Meehl, 1960). Under conditions of uncertainty, mental health professionals may intransigently hold to their initial intuitive judgments even in the face of later evidence that reasonably calls for judgmental change (cf. Tversky & Kahnemann, 1974; Richards, & Wierzbicki, 1990). Further, clinicians may evince an observer attributional bias, a predisposition to ascribe causation to internal patient processes albeit environmental or situational determinants are more reasonably justified (Nisbett, Caputo, Legant, & Marecek, 1973; Witkin, 1982). A central focus on personal determinants rather than the transactional nature of aggressive behavior may lead to clinical underestimates of future violence (Skeen, Mulvey, Odgers, Schubert, Stowman, Gardner, & Lidz, 2005).

Mental health practitioners may also encode selectively information consistent with their hypotheses about the nature of presenting problems while excluding data that are not congruent with presuppositions (Chapman, 1967). Nevertheless, and more positively, there is evidence that training and experience may, to some extent, mitigate judgmental errors and enhance the accuracy of decision-making (see Westen, 2005).

None of the studies reviewed by Meehl or subsequent investigators involved clinical prediction of general intelligence. Indeed, our computer-assisted search (psychINFO), covering over 100 years of psychological and psychiatric research, did not reveal any studies regarding the degree of accuracy of clinical estimates of intelligence.


Virtually all mental status interviews include examining a patientÕs cognitive capacities (Trzepacz & Baker, 1993). Such capacities are likely important in judgments concerning the degree of compliance to medications and the extent to which the patient will likely benefit from certain psychotherapeutic interventions (e.g., cognitive therapies). The clinician queries aspects of memory and executive functions, observes word usage (level of abstraction) and may generate an ordinal type of subjective scale of general functioning ranging from degrees of mental retardation to superior capabilities. Obviously, this is a domain in which accuracy of clinical judgment could readily be ascertained; there is a well-accepted criterion for accuracy, namely the individually administered test of intelligence.

Institutional requirements for mental status examinations at a community mental health center included an estimation of general intellectual functioning. In the current study, patient files covering four years of rendered services were scrutinized.  There were 78 records in which a clinical estimate was made prior to an administration of the Wechsler Adult Intelligence Scale. These estimates were made by experienced clinicians, having at least five years of post-degree employment, representing the areas of psychiatry (four), clinical psychology (five), social work (two), nursing (two), and marriage and family counseling (three). They used somewhat different but conceptually similar phrases in designating levels of intelligence. Numerals were assigned to the verbal estimates as follows:


1 = moderate mental retardation

2 = mild mental retardation; mildly impaired

3 = borderline; below average

4= low average

5 = average; normal

6 = above average; high average; very intelligent


The range of IQ test scores was 46 (moderate retardation) to 122 (superior). Descriptive data are presented below.

Table 1

Descriptive Statistics


  Mean   SD



Est. Intelligence

Obtained IQ







Note. Est. = Estimated on a 1 (moderate mental retardation) to 6 (above average; high average) scale.


A Plot of the estimated and obtained full scale IQÕs suggested a linear relationship. Indeed, as shown in table 2, there was significant linearity in the data. Quadratic and cubic regression yielded non-significant results. The product moment correlation (r) was .698 (p< .01); r2 = .487. Separate correlations for psychiatrists (30 total estimates) and non-medical clinicians (48 total estimates) were .780 (p < .01) and .625 (p < .01) respectively. These correlations were not significantly different (z = 1.27, p>. 05).

Table 2

Linear Regression ANOVA


Sum of Squares


Mean Square
















Perhaps in the domain of intelligence, the experienced clinical human brain may be rather adroit at encoding words of patients that suggest varying degrees of abstraction and concept formation. The clinician may also use standard questions that allow evaluation of long and short-term memory functions. Diagnostic questions may also provide inferences regarding adaptive behavioral characteristics that relate to general intellectual functioning. If our data are replicable, the nature of processing, weighting and combining information considered relevant to general intelligence would be an important task for future investigation. Further, the errors that tend generally to affect judgments may be attenuated in estimating intelligence. Why this may obtain is another intriguing question that might be addressed in the future. Comparisons among clinicians with varying degrees of experience might also be illuminating.   In any event, with almost 50% overlapping linear variance, our data suggest that experienced clinicians may subjectively aggregate information to formulate ÒgestaltÓ judgments that are reasonably accurate in a predictive sense.



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First Published:

May 2006



Steven Thurber, Ph.D., ABPP

Clinical Psychologist

Department of Psychology

Woodland Centers

1125 S.E. Sixth Street

Willmar, Minnesota, USA 56201

(320) 235-4613

Fax: 320-231-9141

Richard Lee, Ph.D.

Clinical Director

Department of Psychology

Woodland Centers

1125 S. E. Sixth Street

Willmar, Minnesota USA 56201

Eugene Bonynge, Ph.D.

Chief Executive Officer

Department of Psychology

Woodland Centers

1125 S. E. Sixth Street

Willmar, Minnesota USA 56201

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