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The field of psychology has always been interested in intelligence, what it is, and how it impacts an individual’s ability to be successful in life. In this lesson, you will meet Charles Spearman and learn about his general factor theory of intelligence and some of his other accomplishments.

Charles Spearman’s Road to Psychology

Charles Spearman, who lived from 1863 to 1945, was an English psychologist who came to experimental psychology a bit late in life.

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He studied engineering in college and worked as an engineer in Burma in the 1880s. In his early thirties, Spearman decided to leave the military to become an experimental psychologist.Spearman headed to Leipzig in Germany to study with the famous experimental psychologist, Wilhelm Wundt, who ran the only PhD program in psychology then in existence. University College, London, hired Spearman as an instructor and researcher in 1907. He worked there for 25 years, rising through the ranks and becoming a very prominent professor of psychology before he retired in 1932. His work influenced a number of important psychologists who came after him.

Charles Spearman
Charles Spearman

Known as an early founder of the psychological testing movement, Spearman refined the methodology of intelligence testing, including the statistical techniques then used to analyze test results. His greatest theoretical contribution was proposing the theory of the g factor, in which he argued that general intelligence formed the bedrock from which all other mental abilities developed.

Bringing Science to the Study of Intelligence

Intelligence is defined as the ability to obtain and use knowledge in a productive way. For thousands of years before Spearman, intellectuals and philosophers worked to understand the concept. Although Spearman loved philosophy, like many others of his generation, he wanted to do more than just talk.

To accomplish this, he brought the scientific method to intelligence testing.For Spearman, understanding why some people grew up to be great thinkers and learners and why other people struggled to grasp even the simplest thing had both practical and philosophical implications. By observing and measuring intelligence in a systematic way, Spearman believed, researchers would be able to define all the variables that influenced the differing levels and types of intellectual ability people have.

More importantly, research would discover how these variables fit together.

Statistical Analysis and Tests of Mental Variables

When Spearman became involved, the psychological testing movement was already underway. Many tests had been developed that looked at different types of intellectual variables, such as math learning or reasoning skills. When psychologists attempted to correlate the results of these tests to one another, they didn’t have much luck. So while Spearman believed that there was an underlying general factor of intelligence that should predict what level of specific mental abilities individuals would show on tests, his colleagues were not finding those relationships in their data. Spearman began to wonder if there was something wrong with the methods his colleagues were using to determine whether relationships existed or not.

At the time, a test called the Pearson Product Moment Correlation was one of the main statistical techniques in use. The Pearson Correlation was named for its inventor, another British academic, Karl Pearson. He based his technique on the concept of correlation first proposed by the great British thinker, Francis Galton.Galton was very interested in heredity, kinship, and the differences between people on a variety of characteristics. His theory was that individual specific characteristics are related to each other, and this ‘co-relation’ would be apparent in the way in which certain characteristics either appeared with others or changed with others.Imagine that you are interested in the correlation of health and intelligence.

If so, you might ask, ‘Does evidence of intellectual ability increase as overall health increases?’ Or, if you were interested in the relationships of reason to emotion, you might ask, ‘Are less emotional people more logical?’ By asking these types of questions, you signal that you believe these aspects of human ability and/or behavior are linked and might vary together in some lawful way.The Pearson Correlation test was a step forward in the analysis of correlation. It was designed to show whether one aspect of human ability was related to another by mathematically plotting the results from one test against the results of another test. Before Pearson’s test was available, researchers checked the amount to which one set of results was correlated to another set by using other types of less sensitive statistical analyses or by manually plotting individual scores from the two tests on a graph like the ones shown here.

Graph of correlations

To make this a little clearer, if the results from Test A plotted along the x-axis of a graph clustered closely to results from Test B, plotted along the y-axis as the first graph shows, a researcher could say that there was a strong correlation between the two sets of results. Another way of looking at that relationship is to say that when there is a strong correlation between two tests, you would expect that almost everybody who had a high score on Test A also had a high score on Test B, and vice versa.

If the results from Test A were weakly correlated to the results from Test B, the researcher would see a graph like the middle image. With that kind of graph, you might find that more of your participants who got a high score on Test A also got a high score on Test B, but not that many more. Finally, if Test A results and Test B results had no correlation to one another whatsoever, plotting them on the graph would yield something like the third image, in which the test results are all over the place and don’t cluster together at all. In that case, you wouldn’t be able to make any prediction about what the scores would be on Test B just by looking at the scores on Test A.The genius of Pearson’s Correlation test was that it allowed researchers to list the two sets of results and then use a statistical formula to determine the level of correlation between the results without having to sit down and plot each individual test result on a graph.

What Made Spearman Skeptical of Pearson’s Test?

Because Charles Spearman believed that general intelligence underlay the specific intellectual abilities people exhibited, he expected that test results should correlate with one another. He also expected that results on tests designed to measure general intelligence should correlate with results of tests on specific abilities. But researchers who analyzed the results using Pearson’s technique did not consistently find the relationships Spearman expected.

He started to think the problem was not in the data, but instead in the method of analysis. So he took it upon himself to examine both the assumptions and the mathematics of the Pearson Correlation.Spearman was able to show that Pearson’s statistic greatly underestimated the strength of relationships between the results of two tests. To fix that problem, Spearman invented a new statistical technique that became known as the Spearman Rank Order Correlation. Using this new technique to re-examine the relationships between different tests of intellectual abilities, Spearman found that, in fact, not only were the results correlated, but the strength of those relationships did indeed provide evidence for his theory of general intelligence.

The ‘G’ Factor and the Human Body

In addition to fleshing out his theory and calling for more research on the relationship of intellectual abilities to each other and to practical measurements of intellectual success, such as grades in school, Spearman also emphasized the importance of finding the physiological correlates of the g factor. He felt it was extremely important to understand how and why processes of the brain and body contributed to the development, decline, strength, or weakness of general intelligence.Although it was pretty impossible to do psychophysiological research in any definitive way given the medical expertise and equipment available in Spearman’s day, his emphasis on the need for this type of research paved the way for modern biopsychology and neurophysiology.

Spearman’s Legacy

When Spearman proposed the concept of general intelligence, his theory was very much in step with the opinions of many of his contemporaries.

Once Spearman refined the statistical techniques in use, the theory was also well-supported by the evidence. But theory and methodology always evolve.Today, most psychologists believe there are a variety of types of intelligence, not just one underlying general factor that impacts on all intellectual abilities.

Even so, Spearman’s work is cited more often now than the work of many of his contemporaries.

Lesson Summary

Charles Spearman was a British experimental psychologist who was active from the early 1900s through the 1930s. He was a founder of the psychological testing movement, instrumental in refining statistical techniques that are still in use today, and a great supporter of research work on the psychophysiological processes that impact on intelligence.He proposed the g factor theory, which holds that an underlying factor of general intelligence exists that forms the foundation out of which all intellectual abilities rise. Spearman also felt that levels of general intelligence could predict levels of specific abilities.Although these days, the theory of general intelligence has been supplanted by a variety of theories that stress different types of intelligence, Spearman’s ideas still contribute to the discussion, and his statistical technique is still in use. He is also still remembered for his early enthusiasm about the potential usefulness of psychophysiological research on intelligence.

Because of the former, Spearman is considered to be one of the founders of the psychological testing movement, and because of the latter, Spearman is also considered to be one of the founders of biopsychology and neurophysiology.

Learning Outcomes

As you finish the video, you should be able to:

  • Explain who Charles Spearman was and how he became interested in psychology
  • Define the g factor and intelligence
  • Discuss how science was introduced to the study of intelligence
  • Examine what the Pearson Correlation was
  • Recognize Spearman’s critique of the Pearson Correlation and the statistical technique he developed in response
  • Acknowledge Spearman’s legacy and what psychologists believe about intelligence today

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