As hiring managers and business leaders, you are tasked with making critical personnel decisions that significantly impact your organisation’s success. The employment interview is likely your most frequently used selection tool. Despite its ubiquity, there is often confusion about what interviews actually measure and how to maximise their effectiveness. This article presents clear scientific evidence to help you understand what interviews really assess and how to design them for optimal hiring decisions.
Method, not attribute
First, it’s essential to recognise that the employment interview is a method — a data-gathering tool — not an attribute itself. When evaluating candidates, you are not measuring their abstract “interview skill”, but using the interview to assess underlying qualities relevant to job performance.
This distinction is crucial for focusing your interview strategy on identifying job-relevant knowledge, skills, abilities and other characteristics (KSAOs) rather than being swayed by general impressiveness or likability.
Think of it this way: When doctors use a thermometer, they are measuring your temperature, not your “thermometer skill”.
Similarly, an employment interview is designed to measure underlying qualities relevant to job performance — KSAOs — rather than simply how well you “interview”.
The power of structure
Research consistently demonstrates that interview structure dramatically affects both what you measure and how well you predict job performance.
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Structured interviews — where questions are based on job analysis, all candidates receive the same questions, and responses are evaluated using specific rating scales — significantly outperform unstructured approaches.
Meta-analyses show structured interviews have an operational validity of approximately 0.44 compared to 0.33 for unstructured interviews, making them about 33% more effective at predicting actual job performance.
For your organisation, this translates to better quality hires and reduced turnover costs.
What you are actually measuring
Scientific meta-analyses have quantified exactly how much different interview types measure various attributes.
Unstructured interviews show moderate to strong correlations with general mental ability (0.41), meaning they are substantially influenced by how intelligent candidates appear.
They also correlate moderately with certain personality traits: emotional stability (0.38), extraversion (0.34), conscientiousness (0.28) and agreeableness (0.26).
For job experience, unstructured interviews show only a modest correlation (0.29) and provide insufficient data to estimate job knowledge measurement.
In stark contrast, structured behavioural interviews measure job-relevant KSAOs much more effectively. They show strong correlations with job experience (0.71), applied social skills (0.65), job knowledge (0.53) and situational judgment (0.46).
Importantly, their correlation with general mental ability is lower (0.28) and they show negligible correlations with personality traits (ranging from 0.08 to 0.21). This demonstrates that structured interviews better isolate job specific competencies rather than being influenced by general impressions or social charm.
Primacy of cognitive ability
It is crucial to understand that while interviews provide valuable insights, cognitive ability measured through psychometric tests remains the strongest single predictor of job performance across virtually all occupations.
Meta-analyses consistently show that general mental ability (GMA) tests have an operational validity of approximately 0.51 for predicting job performance, substantially higher than any other standalone selection method.
Interviews, by comparison, do not measure cognitive ability and personality traits as effectively or efficiently as dedicated psychometric assessments.
For optimal hiring decisions, you should begin your selection process with validated psychometric tests of cognitive ability and personality before conducting interviews. This sequence allows you to efficiently screen candidates on these fundamental predictors before investing in more resource-intensive interviews.
While structured interviews add incremental validity when combined with cognitive ability tests (raising validity from 0.51 to 0.76), the incremental benefit is relatively small compared to the predictive power cognitive ability tests provide on their own.
Question types matter
The questions you ask significantly influence what you are measuring. Situational questions (“What would you do if ...”) measure problem-solving approaches and judgment about future situations, with meta-analyses showing operational validity of about 0.50 for predicting job performance.
These questions particularly measure cognitive processing, situational judgment, and implicit job knowledge. Behavioural questions (“Tell me about a time when ...”) assess demonstrated competencies based on past behaviours, showing validity of about 0.39. These questions excel at measuring actual experience and proven patterns of behaviour in relevant contexts.
Using both types provides complementary insights — situational questions assess potential while behavioural questions verify track record.
Optimal selection strategy
The most effective selection strategy combines psychometric assessments with structured interviews in a deliberate sequence. Start with cognitive ability testing, which provides the strongest foundation for predicting job performance across positions.
Next, consider adding personality assessments that measure job-relevant traits, particularly conscientiousness. Only after these more efficient screening tools have been applied should you invest in conducting structured interviews with your strongest candidates.
This sequenced approach is both scientifically sound and cost-effective. Though structured interviews do add some incremental validity beyond cognitive ability tests, this added benefit is relatively modest and must be weighed against the significant time and resources required to conduct interviews.
For many positions, particularly entry-level or standardised roles, the incremental predictive value may not justify the additional investment in extensive interviewing if robust psychometric testing has already been implemented.
Implementation for business leaders
To maximise the effectiveness of your selection process, begin with validated psychometric tests for cognitive ability and relevant personality traits. Only then develop structured interviews based on thorough job analysis that identifies the critical KSAOs for success in the role.
Create standardised questions — both situational and behavioural — that directly relate to these job-relevant KSAOs. Implement standardised rating scales with clear anchors describing different levels of response quality.
Train your interviewing team to administer the structured format consistently and evaluate responses objectively. Integrate interview results with psychometric test scores for comprehensive candidate assessment.
Conclusion
As a business leader, you understand that talent acquisition directly impacts your organisation’s bottom line. The science is unequivocal: cognitive ability testing provides the strongest foundation for predicting job performance, while structured interviews that systematically assess job-relevant KSAOs can add modest incremental validity when used in conjunction with psychometric assessments.
The unstructured, conversational interviews many organisations rely on provide little value beyond what can be learned from more efficient and objective testing methods.
By implementing an evidence-based selection strategy that begins with psychometric testing and follows with structured interviews for your strongest candidates, you will make more accurate hiring decisions, reduce costly turnover and build stronger teams.
Your competitive advantage begins with how effectively you identify and select talent — and the judicious combination of psychometric testing and structured interviews is your most powerful approach for doing so.
- Nguwi is an occupational psychologist, data scientist, speaker and managing consultant at Industrial Psychology Consultants (Pvt) Ltd, a management and HR consulting firm. — Linkedin: Memory Nguwi, Mobile: 0772 356 361, [email protected] or visit ipcconsultants.com.
