Personality Testing 101 – Why Reliability Matters
Personality insights can have a huge impact on business outcomes – in some research, they’ve been linked to a 40% lift in team performance. That’s no small number. Whether it’s hiring, developing talent, or building better teams, understanding how people operate can make a real difference.
But not all personality assessments are created equal.
As we know, these tools are essentially a collection of data points that aim to help us understand how someone approaches their role, relates to others, handles pressure, leads, and more. That’s important stuff – and the quality of the data behind these insights is what makes them useful… or not.
Understanding the cogs of personality testing is important if you want to really make sure you can maximus the use of its outcomes.
Imagine buying a car and being told it's petrol-powered, only to find out it’s electric once it’s delivered. That mismatch doesn’t just cause frustration – it changes everything about how you plan to use and maintain the vehicle. It’s the same with personality profiling. If the tool isn’t reliable, the outcomes it drives – hiring, development, team design – can quickly go off track. Reliability isn’t a technical detail; it’s the foundation of good decisions.
Today, we want to unpack what makes a personality tool reliable, what can go wrong when it's not, and how to ensure you're using the right tool for the right purpose.
What are the key metrics to look for when it comes to personality?
When evaluating a personality test, two key metrics matter most: reliability and validity:
Reliability is about consistency. If someone takes the same test twice under similar conditions, they should get a similar result. Without that consistency, you're essentially guessing. Here are a few lenses to consider when reviewing how reliably a personality tool is:
Internal Consistency: Are the questions designed to measure the same trait actually aligned? For example, all items measuring “extroversion” should correlate strongly with each other. Industry standard for reliability is 0.70 is considered acceptable while over 0.80 considered excellent (… TALY has a 0.93 score!)
Test-Retest Reliability: Does the tool yield consistent results when the same person takes it multiple times?
Inter-Rater Reliability: If you gathered a bunch of experts on the topic together, would they reach a similar conclusion? (maybe a little more robust than the explanation given here)
Validity is the second metric we like to consider (although we won’t focus on today as much). It refers to whether the test is actually measuring what it claims to. For example, if a tool says it’s measuring resilience, is that backed by research? Valid assessments have strong construct validity and are often supported by peer-reviewed studies.
Remember, a trustworthy provider will be transparent about these metrics. If the data isn’t shared or seems vague, that’s a red flag. Think of reliability and validity as the guardrails that keep personality data meaningful, useful, and fair.
Some tests can be very reliable, but lack validity – meaning they offer no significant insight into the thing they claim to measure so well. For example, star signs are very reliable (your birth date is fixed), but they don’t meaningfully correlate to your love life, job prospects, or well-being at all. This makes validity a key piece of the puzzle, because it lets us translate data into a prediction about behaviours.
By having high reliability and validity, researchers, practitioners, and individuals can be confident that the survey provides meaningful insights into personality traits and behaviours, leading to more informed decision-making and better understanding of individual differences that can contribute to performance, team dynamics and hiring decisions.
At TALY, we pride ourselves in providing reliable insights for you to make your people decisions from. With a reliability score of 0.93, you can have confidence that integrating these insights into your daily work is not only easy, but also ones you can depend on.
Curious to learn more? Let’s chat about how TALY’s tools can help you navigate the complexities of workplace conflict.
Get in touch or book a demo today.
What are the implications of getting it wrong?
Getting personality testing wrong isn’t just a technical issue – it can have wide-reaching consequences across a business.
Unreliable or poorly designed tools can lead to incorrect conclusions about a person’s capabilities and how they think, respond, and interact, which in turn leads to a whole sweep of issues for the individual:
Hire/ Role misalignment: Individuals may not be the best first for the role, not because they lack talent, but because the data that informed the decision was flawed. A misfit hire, a misplaced team member, or a missed leadership opportunity – all can stem from unreliable data.
Missed development opportunities: We won’t know how to support each person in a meaningful way.
Low engagement: We won’t be creating opportunities to best keep people involved or interested.
Employee Discontent: When employees sense that profiling tools are inaccurate or inconsistent, trust breaks down. People may disengage, question leadership decisions, or feel misrepresented.
At the team level, the risks grow. Leaders might rely on inaccurate personality profiles to shape team structure or manage dynamics, only to be blindsided when communication breaks down or collaboration stalls. Mismatched or misunderstood traits can disrupt team dynamics, rather than improving collaboration, unreliable profiling may create friction, confusion, or even resentment.
Worse still, flawed data can unintentionally reinforce bias or create a false sense of certainty, which eventually means unfair outcomes or exclusion for team members – something that has a hugely damaging impact on people and is really hard to undo.
And as you may have guessed, it can also lead to organisation-wide issues. Using the wrong tool – or using it in the wrong way – can scale these issues across an entire organisation. That’s why it's critical to match the tool to its purpose. Some tools are designed for deep psychological insight (like TALY); others are better suited to surface-level communication styles. Using one in place of the other can distort outcomes.
And for a business, there’s also a reputational risk to consider. Employees and candidates are increasingly attuned to fairness and evidence-based practices. If the tools you use feel arbitrary or outdated, it reflects on your brand – both as an employer and as a business that takes people seriously.
The positive impact of reliability
When done right, personality profiling can strengthen business decisions – from who to hire, to how to engage and develop people. It’s not just about fit; it’s about understanding the drivers that lead to performance and potential.
Reliable profiling tools have been shown to reduce the cost of bad hires and boost retention. Some organisations report up to 40% reduction in turnover when they use validated assessments as part of their hiring and development process.
On the flip side, up to 50% of individuals may receive different results when retaking less rigorous tests – highlighting just how unreliable some tools can be.
And it’s not just academic. Reliable personality data leads to better choices, stronger teams, and a more intentional approach to growth:
• Confidence in Decision-Making: Reliable profiling tools provide a solid foundation for business decisions. Whether it’s hiring, assigning roles, or building teams, leaders can act with confidence when the data behind their choices is consistent and trustworthy.
• Building Employee Trust: Employees notice when assessments reflect who they really are. When tools are reliable and used well, people feel seen and understood – not labelled or boxed in. That builds trust, transparency, and engagement.
• Driving Long-Term Growth: Over time, consistent profiling fuels better culture, stronger alignment, and more agile decision-making. The ripple effect of reliable data can shape everything from leadership development to succession planning.
Reliability is not a detail – it’s the foundation. It gives personality assessments their power. Without it, even the most visually appealing reports, clever language, or polished dashboards are just noise masquerading as insight.
They may look impressive, but they won’t stand up to scrutiny or support sound decision-making. With true reliability, however, you get more than data—you get direction. As well as gaining the confidence to act decisively, the clarity to understand what really drives people, and the assurance that your people decisions are grounded in something meaningful and repeatable.