I have written elsewhere on this website about staffing levels and workload – two key human factors topics. In that previous article I outlined some of the signs that might indicate staffing levels are not adequate and discussed the factors to be considered before reducing staffing levels. I also explained how workload can be defined as either the demands that are placed on a user, or as a subjective estimate by those people who are undertaking certain tasks.
People have limited attentional resources, and the demands of a task draw on those resources. How much of that attentional resource being demanded by a task leads to a perception of workload. Perceived (or subjective) workload is an important measure. When workload increases, mental fatigue and stress levels increase, mental health deteriorates and human performance issues are more likely.
One of the most common measures of perceived workload was developed by the NASA Human Performance Group and is freely available. This tool has been used by human factors specialists to assess workload in various environments such as aircraft cockpits, train cabs, Command, Control and Communication (C3) workstations, emergency departments and central control rooms in the oil, gas and chemicals industries. Many studies have shown the NASA Task Load Index to be a valid measure of subjective workload.
This NASA tool is intended to measure subjective workload during a specific activity, event or time period. When people are performing a task, or immediately afterwards, the NASA Task Load Index (“NASA-TLX”) is used to rate their workload on six different dimensions: Mental, Physical, and Temporal Demands; Performance, Frustration and Effort. In my previous article I provided some information on these six rating scales and so I won’t repeat that here.
What people experience as ‘workload’ is a combination of these six factors. The NASA-TLX incorporates individual differences in its definition of workload by presenting participants with pairs of these six dimensions and asking them to choose which of the two is most important for their personal definition of workload. The tool uses this individual assessment to give more (or less) weight to each of the six dimensions when the participant then rates their perception of each factor. Simple, but effective.
The NASA Task Load Index has been provided by NASA as a paper questionnaire for many years, and used to assess perceived workload in different industries around the world. It is one of my favourite examples of how a great piece of research was then turned into a practical tool that could be directly applied by industry. It is an exemplar of how “from research to practice” should work.
But that’s not all. Recently, this really useful tool has received a makeover to become more accessible for a new generation of human factors and safety practitioners. Those clever folks at NASA have created an App, and so the NASA-TLX is now easier to use. The App is available on the App Store for iPhone, iPad, and iPod touch. And it’s free.
Participants can easily complete a NASA-TLX evaluation in their workplace as the App can be used anywhere, even without a network connection.
The original six dimensions are combined into one overall score; however, the App makes it easy to identify where in the six sub-scales the workload may be originating from. For example, on a particular task ‘frustration’ may be more important than ‘physical demands’. This insight can be used to inform changes to the task or situation.
Categories: human factors