Principles of human performance

All workplaces rely heavily on the performance of people – particularly in demanding or high-pressure situations. We also use a wide range of products outside of work, and the usability of these products can be improved with a better understanding of the people that we are designing for.

Many readers will have heard the phrase “human factors” and recognise the need to apply human factors to the workplace, or to the design of things that people use. In order to achieve this, we need a good understanding of what it means to be “human”. Human factors applies an understanding of humans in order to create the best possible fit between people, the things they use and the systems in which they find themselves.

“Human factors discovers and applies information about human behaviour, abilities, limitations, and other characteristics to the design of tools, machines, systems, tasks, jobs, and environments for productive, safe, comfortable, and effective human use” (Chapanis, 1985)

In 2021, the International Civil Aviation Organization (ICAO) published a set of five human performance principles. Even though these were produced for the aviation industry (and more specifically for Regulators of aviation), these five principles apply equally well to all industries. In fact, any workplace where there’s people! They provide a good overview of why we need to take account of human factors.

These principles go some way to explaining human behaviour, particularly in the workplace, but also in other complex environments. They can help us to understand (and optimise) the human contribution to safety.

Considering these five principles in your activities can greatly help to improve the quality of any intervention – whether that’s focussed on health and safety, well-being, quality, usability, productivity, and so on. For example, an understanding of these human performance principles will help to improve the quality of your risk assessments and incident investigations. The principles can also be used to inform the design of products or workplaces.

Understanding and applying these five principles of human performance will improve the reliability of people, by making it easier for them to do the right thing.

Like any set of guiding principles, they should not be considered in isolation – they are interconnected and together they provide an understanding of why people behave the way that they do.

The 5 principles of human performance

Let’s have a look at the principles and then I will unpack each of them in more detail:

1. People’s performance is shaped by their capabilities and limitations
2. People interpret situations differently and perform in ways that makes sense to them
3. People adapt to meet the demands of complex and dynamic work environments
4. People assess risks and make trade-offs
5. People’s performance is influenced by working with other people, technology, and the environment within which they work.

Principle 1: People’s performance is shaped by their capabilities and limitations

This principle is referring to both our physical and mental capabilities and limitations.

We are not always successful in our tasks – our performance can be variable. This variability may be due to features of our work and workplace, or human performance may deteriorate due to stress, fatigue, or illness. We are unable to sustain high performance for long periods of time (such as on a monitoring task). Performance is heavily shaped by the need for oxygen, rest breaks, sleep and nutrition. When these needs are not met, human performance degrades rapidly. Other physical limitations include a limited ability to see in the dark, or lift heavy objects.

People also have cognitive limitations (e.g., relating to perception, attention, memory) that constrain what people can perform. We cannot remember everything that we have seen, read or been told. We’re unable to perform complex mental calculations and human performance degrades if our workload is too high.

To save mental resources or energy, we often use mental shortcuts (known as heuristics), but these are not always appropriate. We make assumptions that may not be correct. This can lead to bias in our decisions and we may make poor choices. The “fast thinking” approach (when we’re making quick, automatic responses) may dominate thinking, and this approach will not always lead to the best outcome. People have difficulty in judging the probability of events, and often underestimate risk in familiar situations.

Our performance is also shaped by our mental state. Psychological conditions, emotional state or intrusive thoughts can impact on our mental well-being, which in turn will affect our task performance.

These capabilities and limitations may change as we get older. And although some influences on performance are permanent (part of what makes us human), some may affect us only temporarily, as we experience life’s ups and downs.

It’s key to acknowledge that all humans have physical and cognitive limitations, and that they cannot be overcome simply through willpower. Telling people to try harder, be careful, or work safely will not compensate for these human characteristics.

Principle 2: People interpret situations differently and perform in ways that makes sense to them

Given different backgrounds and experiences, people will form different understandings of the information presented to them. Based on this understanding, people will act accordingly. Therefore, people will generally do what “makes sense” to them. On the whole, people aim to achieve a good outcome for themselves, their team and the company that they work for. So we can assume that for the majority of the time, most people have good intentions.

“Different people will react in different ways to the same situation”
(Reducing error and influencing behaviour, HSE, 1999, p.23)

When interpreting a situation, people use knowledge of what has happened before, refer to procedures or a manual, as well as what they currently perceive in the world around them (e.g., what they can see, hear, smell or feel). They may look for patterns that align with their experience, be influenced by their trust in information – and maybe with a little intuition – make sense of the world around them. People often make choices based on limited information.

Principle 3: People adapt to meet the demands of complex and dynamic work environments

Work and workplaces are often described as dynamic, meaning that the circumstances and demands are changing. For example, there may be changes in weather, team members, availability of systems and equipment, or time available. Rules and procedures may not be fully applicable (or may not even exist for the situation that people find themselves in). Designers cannot imagine all possible applications for their products or systems. The various departments or organisations involved in an activity may have different goals or cultures. Not everything happens as predicted.

However, people are often successful at work (and other pursuits) in the face of imperfect systems, processes and equipment. We are adaptable, resourceful and creative. When placed in a novel situation, we can adapt and improvise.

People may choose not to follow a procedure if they consider that it is not appropriate for the circumstances. This is related to Principle 2 in that people do what makes sense to them, given what they currently understand, even if that means choosing a “work-around”. Usually, these work-arounds ensure that the company goals are met. (However, they may be seen as a non-compliance issue should an incident occur).

People are required to adjust and adapt to these changes. Due to these adaptations, “work as performed” may be quite different from how the work was planned. Despite this, the resilience and resourcefulness of people usually ensures that the work still gets done successfully. People are good at managing difficult situations with incomplete information.

In the past, the human contribution to safety often focussed on human failures (and how errors and violations adversely impacted safety). However, recent focus has been on the positive contribution that people bring to safe operations and their ability to adapt, despite changes and challenges. Human factors specialists aim to understand not just the occasions when things go wrong, but also why they (usually) go right. Although people may be seen as a cause of incidents or a source of risk, they are, more importantly (and more frequently) the source of success through good performance.

People are pretty good at adapting to changing demands!

Principle 4: People assess risks and make trade-offs

People assess risks and trade-offs differently, based on individual characteristics, personal experience, motivations and socio-cultural factors. The choices that people make will also be influenced by incentives and what they perceive to be important – for example, real or perceived pressure to meet production or efficiency targets. In the workplace, the words and actions of leaders will contribute to an understanding of priorities. If people have been deviating from a procedure without incident on many occasions, their perception of the risk may be quite different to someone who recently experienced an incident.

In order to address conflicting goals, people may have to trade one objective against others. This may involve balancing speed versus accuracy, or short-term versus long-term benefits. People will, based on their perceived level of acceptable risk, attempt to come to a compromise. Issues can arise when people focus on achieving one goal (e.g., efficiency) at the cost of another goal (e.g., safe operations).

Company leadership may see the primary risk as “potential to result in harm to people“, but team members may perceive the risk of “failing to meet end-of-month targets” as more important. Therefore, the trade-off equation may vary between individuals, between teams and at different times.

The trade-off between two variables can be illustrated if we ask people to complete a simple task as well as they possibly can. These individuals have the choice to optimise accuracy, optimise speed, or a combination of the two strategies. Depending upon the strategy chosen, the extremes could result in very fast performance with many errors, or slow performance with few errors. Real life, however, may involve more than two conflicting goals.

Principle 5: People’s performance is influenced by working with other people, technology, and the environment within which they work.

People do not work in a vacuum – they are part of a wider (and possibly complex) system. How people perceive the world and respond to it can be heavily influenced by other aspects of that system. These influences can have a positive or negative impact on human performance. For example, being a part of a group may enable an individual to make better decisions, or the cognitive bias of “group think” may result in a poor decision, as people try to reach a group consensus.

Working with other people can be a strength, because a diverse team can compensate for the limitations of individuals – whether that is their physical or cognitive capabilities. The culture of a company, or a team within it, will influence behaviours. The safety culture of an organisation affects how safe behaviours are valued and prioritised, and therefore has a significant influence on people’s performance. For example, if supervisors appear to condone unsafe behaviour in order to achieve production goals, then safe behaviour will be less likely. Or if few other people wear hearing protection in a noisy environment, this may discourage safe behaviours.

Technology that has been designed with people in mind may lead to improved performance, whilst the introduction of some technologies (such as automation) will change the nature of roles and responsibilities – not always for the better.

The physical environment in which people work can influence their performance, which is why there are standards for physical conditions such as lighting, temperature, vibration, and work space. We know that people can perform better when these conditions are optimal. The weather can also have an impact on our performance.

Practical applications of the 5 principles

These principles are essentially just theory – unless they are addressed in practice.

Considering the five principles of human performance in your management system or business processes can enhance the effectiveness of your activities. Below, I have outlined three possible applications of these principles to help embed them into your systems.

Design of products, systems and facilities

A better understanding of human capabilities and limitations in design can improve the “fit” between people and the products or facilities that they use. This is often called Human-Centred Design. When design is centred on the needs and capabilities of users it will reduce human failures, ultimately creating a more resilient system. Poor design can often be identified in the workplace where people have adapted equipment – such as extra labels on switches, or blocks of wood that act as steps to reach equipment. Several articles under the Human Factors Integration topic provide more details on how to design for people.

As well as “designing out” human performance issues, we can also “design-in” error tolerance. This means that even if errors do occur, they will have less impact. In other words, the system can cope with human errors, or the consequence of errors is reduced (known as “fail-safe design”). As a Government inspector of oil and gas facilities, one of my guiding principles was that a human failure should not be able to lead directly to a major incident. The facility and systems should be designed with several layers of defences, or layers of protection. If you know what the likely human performance issues may be, you can build stronger defences into the design.

In designing things for use by people, it’s important to recognise the characteristics of the actual user group. Just because you can reach a key control, or understand a set of instructions, does not guarantee that the end users will. To quote from one of my old textbooks:

“Simply being a human being does not make a person a qualified human factors specialist”
(Human factors in engineering and design, Sanders and McCormick, 1987, p.6)

The design of work and jobs can also significantly affect human performance. For example, work that is not stimulating, with little autonomy, unclear objectives and high time pressure will negatively impact human performance (and mental well-being). How to design “good” work is considered in detail in this article.

Work planning and risk assessment

Applying these principles in work planning can ensure that work activities are compatible with human capabilities, that procedures support people, training is appropriate, the pace of work is suitable and there are sufficient resources to undertake the work (including dealing with unexpected situations). More information is available on all of these factors under the “Key Topics” pages.

For example, if an activity relies on someone remembering multiple task steps, a checklist may be used to address memory limitations. And if a critical activity requires a high degree of alertness, the shift pattern and rest breaks can be optimised to support task performance.

Thinking about potential human factors problems and planning ahead is more effective than waiting for problems to occur and then fix them after the event. Refer to the “Hierarchy of Controls” when choosing precautions, and try not to rely on human performance to control a workplace hazard.

In assessments of human reliability, the limitations of people are a type of Performance Influencing Factor (PIF) that, when combined with other factors, can increase the likelihood of human failures.

Insights from the five principles can ensure that risk assessments are based on the realities of human capabilities and limitations, how people work, and the challenges that they may face. These assessments will then better reflect how work is really done. The more that people are prepared and supported, the greater the likelihood that they will be able to perform their tasks efficiently and safely. Prior to work commencing, the input of those who actually do the work can help to identify any aspects that are not a good “fit” with ideal human performance (e.g., gather input at toolbox talks or pre-start meetings).

Incident investigations

Given the above principles, we can conclude that humans are not perfect. Due to these limitations, influences, adaptations and interactions, people may perform differently to how was planned or expected.

When we look back at incidents (with the benefit of hindsight), it can be tempting to criticise the decisions that people made, or the actions that they took. However, at the time, in the heat of the moment, those decisions and actions seemed appropriate to those involved. They made sense at the time. Otherwise, people would not have behaved the way that they did!

This is why it is important in incident investigations to identify what information was available at the time, and to understand how it was interpreted by those present. In an investigation, with more information available – and more time to consider it – we may have a different interpretation.

Incident investigations should aim to identify the reasons for behaviours – examining the “context” that helps to explain why people performed in a certain way. The investigation may identify that in the same circumstances, an individual’s peer group would have likely behaved in the same way (the “substitution test”).

A better understanding of these five principles of human performance will avoid labelling incidents as being due to “human error” and enable a deeper assessment of why errors occur.

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