Virtually the first thing occupational psychology MSc students learn in their selection and assessment modules is the predictive validity of ability tests (also known as aptitude tests, cognitive ability tests, general mental ability tests etc). We learn very early on that general cognitive ability, as measured by a battery of ability tests (such as verbal, numerical, and abstract reasoning tests), are the strongest predictors of performance known (Schmidt and Hunter, 1998; Schmidt, 2016).

In fact, more recent revisions of this research suggest that cognitive ability tests are even more predictive of future performance than previously believed:

As you can see, ability tests are by far the strongest predictors of performance, outperforming assessment centres, job try-out procedures, and even interviews when it comes to predicting job performance.

Perhaps more importantly, research suggests that this correlation is even stronger in highly complex professional and managerial work (Schmidt, 2016), making ability testing absolutely essential in white-collar selection and assessment programmes.

The empirical evidence for using ability tests in recruitment is overwhelmingly strong and draws from almost a hundred years of research. Perhaps the best summary of this research was provided by Professor Frank Schmidt:

“The purely empirical research evidence in I/O psychology showing a strong link between general cognitive ability (GCA) and job performance is so massive that there is no basis for questioning the validity of GCA as a predictor of job performance”

Although the empirical evidence is virtually indisputable, the theoretical basis for why ability tests predict performance is less well known.

As a quick summary of the theoretical case, there are three main reasons why and how cognitive ability predicts future performance in the workplace:

Complex Problem Solving

Perhaps the most obvious explanation for cognitive ability’s predictive power is complex problem-solving ability. Ability test questions are literally cognitive problems, and the ability to solve them is a direct measure of one’s problem-solving ability.

Greater cognitive ability allows people to solve problems faster and more effectively, granting a tremendous advantage in the workplace. Similarly, those that genuinely score low on cognitive ability tests show reduced complex problem-solving ability, taking longer to solve problems or failing to solve them at all (or indeed make them worse).

Research shows that cognitive ability is highly correlated with problem solving ability, and cognitive ability is particularly associated with the following performance appraisal items (Gottfredson, 1997):

• Deal with unexpected situations (.75)
• Able to identify problem situations quickly (.71)
• React swiftly when unexpected problems occur (.67)
• Able to apply common sense to solve problems (.66)
• Able to compare information from two or more sources to reach a conclusion (.49)

This relationship between problem solving and cognitive ability is particularly powerful in complex professional / managerial level work, where this relationship is strongest (Schmidt and Hunter, 1998). Naturally, the problems facing professionals, managers, and highly technical workers require significant cognitive input, granting a massive advantage to those with higher levels of cognitive ability.

Learning and Knowledge Acquisition

Another major reason behind cognitive ability’s predictive validity is its influence over learning and knowledge acquisition.

Ability tests require test takers to understand information presented to them. For example, a numerical reasoning test may present a table of numerical data, verbal reasoning test may present a written passage of information, inductive reasoning tests present a logical sequence of images etc.

This ability to understand and correctly interpret information translates very well to learning and knowledge acquisition, as made evident by the large correlation between cognitive ability score and training performance (Schmidt and Hunter, 1998; Schmidt, 2016).

Research also shows that cognitive ability is associated with the following performance appraisal items (Gottfredson, 1997):

• Able to learn and recall job-related information (.71)
• Able to learn new procedures quickly (.66)
• Alert and quick to understand things (.55)

The greater a person’s ability to acquire job-related information, the greater their eventual performance in the workplace. This is particularly important in graduate schemes, where new hires must learn a great deal of new information within a set time-frame.

This also means that organisations generate a greater ROI from their training programmes after hiring candidates using cognitive ability tests. This is because employees will retain more information during their training programmes, acquiring more job related knowledge and improving their performance to a higher degree.

Objectively Correct Answers

Ability test questions have the advantage of being, for the most part, objectively correct or incorrect. This is particularly clear with numerical reasoning tests, where the correct answers are ascertained using indisputable mathematics.

Contrast this with employment interviews, whereby the interviewer’s subjective biases, opinions, and even current mood massively effect an interviewees rating, inevitably reducing the reliability of the interview method.

Having objectively correct or incorrect answers provide at least two major benefits when using cognitive ability tests in employee selection.

Firstly, it increases the reliability of the assessment. Statistically speaking, this ensures a quantifiable level of precision, allowing assessors to make surprisingly accurate (but by no means perfect) estimates of a candidate’s ability.

Secondly, it makes ability tests very straightforward to troubleshoot during the assessment design process. Item analysis statistics readily identify problem questions, ensuring an unparalleled degree of quality control in the finished product compared to other selection tools. 

Summary

Although the validity of cognitive ability as a selection tool is indisputable, the theoretical explanation of why this is the case isn’t as well known.

The three most salient reasons behind the predictive validity of cognitive ability in the workplace i.e. problem solving ability, knowledge acquisition, and the reliability associated with objectively correct answers, more than explain why ability tests are such strong predictors of performance.

Perhaps more importantly, these reasons make intuitive sense based on our understanding of cognitive ability as a psychological contrast. Naturally, smarter people are better able to solve problems and learn, that is intrinsic to the nature of intelligence as we all implicitly define it.

Lastly, although it may seem trivial at first, utilising objectively correct and incorrect answers makes a big difference. Although psychological measurement cannot match the precision seen in the physical sciences, cognitive ability tests represent perhaps our closest attempt, providing scores which are more meaningful than any other psychometric assessment method.

Final Thoughts

It’s worth mentioning that there are almost certainly more reasons why cognitive ability predicts job performance.

For example, the research on cognitive buffering suggests that cognitive ability can be used to buffer personality traits i.e. enhance resilience, conscientiousness, or negate the negative effects of neuroticism.

Similarly, the specific abilities measured in cognitive ability tests may have an impact i.e. those scoring particularly high on numerical reasoning tests may be better suited to quantitative fields, independent of their overall cognitive ability.

If anyone has other major explanations for the predictive validity of cognitive ability, I would love to hear them in the comments section!