The 7 Steps of Hierarchical Task Analysis: Part 3

This is the third in our series of blog posts to teach you the basics of Hierarchical Task Analysis.  In our first two posts in this series, we explained exactly what Hierarchical Task Analysis is and how to set context and boundaries for your analysis. In this post we are going to focus on how to collect information for your analysis. 


1. Speak with Subject Matter Experts.  You need to call on the necessary technical specialists to be able to produce an accurate description of the tasks. The quality of your task analysis will depend on close liaison with the Safety Case Team, for safety case support, or with designers, during design assessment. They will often be able to provide you with:

  •  Detailed objectives for the analysis
  •  Necessary documentation
  • Technical knowledge

You may find it preferable to use one person within the safety case team or design team as your liason. This person can then arrange and manage access to other necessary specialists as the analysis develops.  As a human factors specialist, you may need to interview actual operators or observe them at work. If you are granted time with skilled and experienced operators, remember operating crews in all industries are kept to a minimum, so your time with them may be very restricted. You should carefully assess the need for operator access and minimize the requirement. Any work should be well planned so that there are no delays and thus any access to experienced staff is fully exploited. 

Time spent up-front deciding who will provide the most useful information and being prepared to discard questionable results will pay large benefits in the future. In the early stages of the work, identify the key users or subject matter experts, then cross-check throughout the interviews about experience, the names of other people involved but not central to the task, and people who are involved in the task for only some of the activities. 

2. Study existing documentation and training materials.  A study of the existing documentation and training will provide a foundation for discussion during the interview and may help in the identification of different types of people to interview. This can include functional descriptions, system descriptions, interface layouts, plant and instrumentation diagrams (P&ID), flow charts, and logic diagrams. It is important to ensure that these are representative of the current situation, or the latest design proposals.

3. Review Task Records.  It is also valuable to review task records. These include procedures, training documentation, logs, checksheets, operational feedback records, and critical incident reports. These indicate how tasks should be undertaken, or how they were undertaken in the past. Consider reviewing safety documentation such as safety reviews and incident reports. 

4. Conduct Interviews. If you are analyzing an existing system it is important to gain the trust of the interviewee so that they will tell you how the task is actually carried out, not how it is supposed to be carried out or what the manual says. The difference is critical to identifying where the current system makes work difficult for the user.

5. Hold group discussions.  Table-top discussions involve a selected group of experts discussing specific operational or technical issues. Such discussions are usually structured upon a specific procedure or scenario. 

6. Observe Task Performance.  Task performance can be observed whilst undertaking a task on a simulator or on the real system. 


Let's review our example's context.  You are a human factors engineer in a company that makes cars, and you are assigned to a team that is designing a website to help users with any questions they may have about their cars. You have already established the following in Step 1:

  • Goal:  Reduce demand placed upon customer support by providing a web based resource to answer frequently asked questions.
  • Stopping Rule:  Stop breaking down tasks when the task can be completed by the most unfamiliar of customers.
  • Properties: Expected time to complete, tools required, difficulty level of overall task, difficulty of individual task, importance, frequency, training content.


We already know our customer support teams are busy so we first do our homework.  If you try searching on the web with some phrases like "common reasons to call your car company for support" and "top reasons for looking in your car's user manual" and you might see this post: The 10 Most Important Things in Your Car Owner's Manual.  For the sake of brevity, we'll use this as a key piece of information.  I would also expect that we would look at our customer support center email records and speak with call center employees to refine our list.  Here is the list we might settle upon for important content for our website (taken from the website above):

  • How to Set Up Your Car
  • How to Check Your Fluids
  • How to Drive Your Car Better
  • How to Troubleshoot Common Problems
  • What is your Car's Frequently Used Technical Data
  • How to Achieve Ideal Tire Pressure
  • How to Keep Your Car Looking It's Best
  • What Does this "Fill in the Blank" Do
  • What Does My Warranty Cover

Of course, each of these task needs to be broken down further until the stopping rule is satisfied.  In this case, the task needs to be described in the terms that an unfamiliar customer can understand.  For example:

  • How to Set Up Your Car
    • How to Set Your Clock (Do all in order)
      1. Turn the vehicle on
      2. Push and hold the display button
      3. Observe the dashboard display window change to the "Setting" display
      4. Observe whether option "Clock," "Display," or "Return" is highlighted
        1. If "Clock," is highlighted, push and hold Display until display changes again.
        2. If "Display" or "Return" is highighted
      5. etc...


You are now well on your way to performing your first HTA.  You are ready to move on to the next step in Hierarchical Task Analysis, verifying the information you collected.