How to Judge if Someone is Trustworthy using the Trust Equation

How to measure trust using the trust equation
Photo by Sora Shimazaki via Pexels

The essential elements of trust in any working relationship

You are away from home and need to go and see a doctor. How do you know whom to trust to help you? You look up local clinics on the internet and find two options. On one website there is a picture of someone, straight-faced, in casual clothes, accompanied by a short statement of them telling you how good a doctor they think they are. The other site has a picture of a smiling doctor (we know this as they are wearing a white coat with a stethoscope draped around their neck). In the background, we can see various certificates and below the picture is a description of how the staff care about you and your well-being. Which doctor do you choose? Which do you trust?

This is a hypothetical example, but it does demonstrate that knowing whom to trust is a vital part of our decision-making. Therefore, it is no real surprise that neurologically we have developed powerful mechanisms to assess how trustworthy people are. But explaining how this psychology works is slightly harder as the brain works largely intuitively in assessing whether we should trust someone or not. 

Fortunately, research has shown that there are common elements at work when we analyse trust. Whether that is for a person we have just met or someone we have known or worked with for a while, it turns out that this feeling is based on some factors that can be measured. And this is where the Trust Equation comes in.

The Trust Equation – understanding the psychology of trust

The Trust Equation was developed by Charles H. Green, co-author of The Trusted Advisor, along with David Maister and Robert M. Galford. They explored the psychology of trust by looking at professional services and how people relate to one another. The result of this study was the Trust Equation. 

The equation is actually a measure of trustworthiness, in other words, how much trust we are willing to invest in a person. In this context, to have trust between two parties, you need someone who is trusting and another person who is trustworthy. The equation gets to the heart of that relationship.

Equation of Trustworthiness:

Trust (or Trustworthiness) = (Credibility + Reliability + Intimacy)/Self-Orientation

The Trust Equation
The Trust Equation

For clarity, it is worth exploring the terms that Green uses in the equation as some may not be immediately clear. To make things very practical, here are some questions you can ask to think about how someone might score against each of these terms. 

Credibility (words)

  • Is the person professionally credible; do they live up to their CV?
  • Do the person’s words fit their actions?

Reliability (actions)

  • Are they dependable? 
  • Will they do what they promise?

Intimacy (feelings)

  • Do you feel safe or secure around the person?
  • Do you trust that person with confidential or personal information?


  • Is a person self-centred, putting themselves before the needs of the vision and team?
  • Are they self-obsessed (always framing an issue from their own perspective) or do they look at a situation more broadly?

As mentioned before, our brains usually intuitively make this calculation but, with the equation, you can quantify each factor by giving it a numerical value (1-10) for the answer to each question. 

The Trust Equation (explained in less than 5 minutes)

Examples using the Trust Equation

Let’s explore this with a couple of examples.

Example 1

Firstly, let’s examine how we might perceive the local barista who serves us our coffee in the morning. I am thinking of one in my favourite coffee shop. How do they score on credibility? Well, their claim to be a barista is backed up by the fact that they work in a good café, and I have seen them serve great coffee. Therefore, let’s give them 8 out of 10. In terms of reliability, whenever someone asks for their double-shot latté that’s exactly what they get (and it tastes good too!). So, 9 out of 10 here. In terms of intimacy, I don’t know them well enough to share all my personal life with them, but they do smile, say a warm hello and address me by my name. They make me feel good, thus, let’s make that 7 out of 10. By contrast, the score for self-orientation will be low as whenever I see this person, they are always serving other people. They are asking what other people want, not talking about themselves, so we can give them a 2 out of 10. Using the equation this becomes:

(8+9+7)/2 = 12

Example 2

Now let’s take a contrasting situation. Picture a politician whom you know of but don’t necessarily follow closely. I have one in mind. This person has been a politician for some time so there is credibility there, but they have also changed their messaging on certain issues. So, for credibility, we can give them a 6. This variation in what they say and do also impacts their reliability score as I don’t feel that they will do as they promise. Therefore, this might be a score of 5. In terms of intimacy, I don’t feel I have any real connection with this person. Would I feel safe with them? I would like to think so, but I still can’t give them more than a 6. For self-orientation, the score must be higher than the barista as, even though they are a public servant, I recall that when I have seen them in interviews, they are often defending themselves. Thus, here I would give them a 7. Now, using the equation we have:

(6+5+6)/7 = 2.4

How do we compare trust equation scores?

This prompts some interesting reflections. The scoring indicates that I trust the barista more than four times more than the politician. In some ways, this is true as I have a closer personal relationship with the barista, even if it is just because we know each other’s names. And I really like coffee.

But here we expose a problem. Even though we are giving a quantitative score to trust, this is impacted by qualitative feelings and influenced by cognitive bias. The barista gives me a lovely coffee every time I see them. That has a powerfully positive anchoring effect. By contrast, the politician suffers from negativity biasas I see them on the news which is emotionally negative. Also, if I am honest, I go to that coffee shop as it is the sort of place ‘people like me’ go to. This means I have an in-group bias towards that barista, but an out-group bias against a politician that belongs to a political party I don’t usually support. 

Finding the right comparisons

Here we have illustrated what is good news for baristas but a perennial problem for politicians. We generally love the experience of getting a coffee but are less keen on politics. As our elected leaders feel ever more distant, and all we see are the U-turns in policy or the sound bites on the news, it becomes very hard to build trust with the electorate. 

By contrast, we might feel that we generally trust doctors or teachers, but that is often because we have some personal contact with these people and even if we don’t know them personally we hold their qualifications (and therefore their credibility) in high regard. 

It is important to note that this comparison of the barista to a politician is also unfair. Trust is also contextual. If the barista suddenly ran for political office, then we are likely to see their scores change, particularly in the realms of credibility. A fairer, and more useful comparison would be scoring one barista against another and one politician against another. That better explains why we might choose one café over another or vote for one representative rather than another. 

Applying the trust equation

We all have an intuitive feeling when we trust people but sometimes, particularly when we are unsure of our feelings, it is worth quantifying them. Understanding the trust equation can help do just this and assess the levels of trust that you have with an individual or team. 


Trust (or Trustworthiness) = (Credibility + Reliability + Intimacy)/Self-Orientation

Why not experiment with the equation now? You can score someone you are thinking about (to better analyse that relationship) or you can score your team culture to examine the levels of trust within your workplace. Finally, you can also use this as a self-reflection exercise and examine how you perform in each area. Remember to think of evidence – of actual experiences – to back up your scores.

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