IQ, Reaction Time, and Mortality: A Critical Review

Introduction to Intelligence and Its Definitions

All learning, on the basis of one's composite mental ability structure, can be thought of as a puzzle intricately shaped by neurological, physiological, psychological, and sociological factors. When blended together, these factors produce a healthy, functioning individual. Therefore, before an understanding of how learning comes about — or what variables affect its outcome — one must first understand the concept of intelligence.

Most individuals, professional or lay, have an almost intuitive sense of what constitutes intelligence. Broadly defined, intelligence is an individual's total ability to solve problems. The more complex the problem, the more it is assumed that the individual possesses a higher level of intelligence. Unfortunately, most definitions do not differentiate between intelligence as a general ability and intelligence as several independent systems. That is to say, the question remains: is intelligence a resource of the brain, a particular characteristic of learned behavior, or a finely tuned set of skills and content knowledge?

Although there is no widely accepted definition of intelligence, the most acceptable working definition is that of knowledge inclusiveness. This means that the amount of information an individual has retained and applied — as measured by some standardized assessment instrument — serves as a measure of intelligence level. Whether test scores from these instruments actually reflect an individual's intellectual level has been, and will continue to be, a prime target of debate. The question will always remain as to whether the amount of knowledge one has acquired truly constitutes one's level of intelligence. For a broad overview of how intelligence is defined and measured across disciplines, Wikipedia provides a useful starting point.

Overview of the Deary and Der Study

If one favors the definition that intelligence is the total composite of what has been learned, then a necessary requirement for acceptance lies in understanding how the information was learned. By reviewing a selected journal article, this paper focuses on the "how" of learning and its relationship to intelligence; how effectively intelligence is — and can be — measured; and the limitations of the Intelligence Quotient (IQ) with respect to an unusual dependent variable: death.

Deary and Der authored the article chosen for review, entitled "Reaction Time Explains IQ's Association with Death," published in the Psychological Science journal of the American Psychological Association (2005). The article was chosen not only for its topical uniqueness but also for its research design and the questions it raises about the relationship between cognitive performance and longevity.

Major Methodological Issues

Any research endeavor must stringently adhere to a protocol that outlines the investigators' purpose, a well-defined research question, a testable hypothesis, and appropriate data analysis. The Deary and Der article, although investigatively sound in several respects, failed at the outset to define either the theory of intelligence or the concept of intelligence itself. As the authors were attempting to determine whether an association (correlation) exists between intelligence and death, they were obligated to define all variables present in the investigation. Such definitions are especially necessary when conclusions are drawn and inferences are made about the association between IQ and death.

The authors would have been well advised to define their concept of intelligence — whether cognitive, neurological, or sociological. Without a clear definition of the theory of intelligence, the reader is at a loss as to which subcomponents are relevant to the relationship between intelligence and death. For example, had the authors chosen a cognitive approach to intelligence, the mental abilities comprising the g factor (verbal, performance, mathematical, spatial, etc.) should have been referenced as secondary relationship variables. A helpful reference for understanding the g factor in psychometric research clarifies why such specification matters methodologically.

Not only do the authors fail to provide an appropriate cognitive definition of intelligence, but they also label the intelligence construct as belonging to "cognitive epidemiology." This creates a somewhat contradictory framing. How can cognition — that is, the ability to think and reason — be treated as a disease? Given that the authors are studying the relationship between intelligence and death, they would have been better served by omitting the term epidemiology from the research framing altogether.

Conclusion

Although the Deary and Der study is somewhat novel, credence must be given to the authors for taking on such a research endeavor. Even though they did not adequately define the concept of intelligence or clearly describe their measurement instrument, they have nonetheless opened an area of research that offers no boundary. Should additional research be conducted using other IQ measurement instruments, along with more rigorous statistical analysis tools, the concept of intelligence will take on an entirely new meaning for parents, educators, psychologists, and physicians alike.