Critical Incidents Technique

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Despite numerous variations in procedures for gathering and analysing critical incidents researchers and practitioners agree about the definition of what critical incident technique (CIT) analysis should do:

The critical incidents technique can be defined as a set of procedures for systematically identifying behaviours that contribute to success or failure of individuals or organisations in specific situations.

In real world task performance, users are perhaps in the best position to recognise critical incidents caused by usability problems and design flaws in the user interface. Critical incident identification is arguably the single most important kind of information associated with task performance in usability -oriented context.

Several methods have been developed for conducting usability evaluation without direct observation of a user by an evaluator. However, contrary to the modern 'user reported critical incident method', none of the existing remote evaluation methods (nor even traditional laboratory-based evaluation) meets all the following criteria for a successful CIT analysis:

Data are centred around real critical incidents that occur during a task performance
Tasks are performed by real users
Users are located in their normal working environment
Data are captured in normal task situations, not contrived laboratory settings
Users self report their own critical incidents after they have happened
No direct interaction takes place between user and evaluator during the description of the incident(s)
Quality data can be captured at low cost to the user

Typical application areas:

Useful for obtaining in-depth data about a particular role or set of tasks. Also extremely useful to obtain detailed feedback on a design option.

The basic steps involved are:

Gather facts (incidents) about what actually happened
after the incident
Analyse the content of the verbal report
Infer how to improve performance based on the above feedback

Step 1:Gathering facts

The methodology usually employed is an open-ended questionnaire, gathering retrospective data. The events should have happened fairly recently: the longer the time period between the events and their gathering, the greater the danger that the users may reply with imagined stereotypical responses. Interviews can also be used, but these must be handled with extreme care not to bias the user.

Example of a moderately structured approach:

We'd like you to think of what was happening when you were (carrying out activity X). What lead up to the situation? Did you do anything that was especially effective or ineffective? What was the outcome or result of this action? Why was this action effective or what more effective action might have been expected? Please write about them in your them in your own words using the form below.

Example of a moderately unstructured approach:

Please write down two good things that happened when you were (carrying out activity X), and then two bad or unhelpful things.

CIT generates a list of good and bad behaviours, which can then be used for performance appraisal.

Vague, generic answers suggest:

poor focus of study to begin with
inaccurate perceptions/memory in users
response bias or cultural norm responding

Step 2: Content analysis

Subsequent steps in the CIT consist of identifying the content or themes represented by clusters of incidents and conducting "retranslation" exercises during which the analyst or other respondents sort the incidents into content dimensions or categories. These steps help to identify incidents that are judged to represent dimensions of the behaviour being considered.

This can be done using a simple spreadsheet. Every item is entered as a separate incident to start with, and then each of the incidents is compiled into categories. Category membership is marked as:

quite similar
could be similar.

This continues until each item is assigned to a category on at least a 'quite similar' basis.

Each category is then given a name and the number of the responses in the category are counted. These are in turn converted into percentages (of total number of responses) and a report is formulated.

Step 3:Creating feedback

It is important to consider not only the bad (negative) features of the report, but also the positive ones, so as not to undo good work, or to make destructive recommendations.

The poor features should be arranged in order of frequency, using the number of responses per category. Same with the good features.

Go back to the software and examine the circumstances that led up to each category of critical incident. Identify what aspect of the interface was responsible for the incident. Sometimes one finds that there is not one, but several aspects of an interaction that lead to a critical incident; it is their conjunction together that makes it critical and it would be an error to focus on one salient aspect - for instance, to focus on the very last event before the incident when a litany of errors has preceeded it.

Drawbacks of the method

  1. It focuses on critical incidents therefore routine incidents will not be reported. It is therefore poor as a tool for routine task analysis.
  2. Respondents may still reply with stereotypes, not actual events. Using more structure in the form improves this but not always.
  3. Success of the user reported critical incident method depends on the ability of typical end users to recognise and report critical incidents effectively, but there is no reason to believe that all users have this ability naturally.

Evidence in support of the method

  1. Nevertheless, a case study conducted by Hartson et,al. (1996) obtained detailed factual information about pilot error experiences in reading and interpreting aircraft instruments from people not trained in the critical incident technique (i.e., eyewitness or the pilot who made the error)
  2. Users with no background in software engineering or human computer interaction, and with the barest minimum of training in critical incident identification, can identify, report, and rate the severity level of their own critical incidents. This result is important because success of the use reported critical incident method depends on the ability of typical users to recognise and report critical incidents effectively. (Hartson, R.H and Castillo, C.J, 1998)

Variations on the method

Several human factors and human computer interaction researchers have developed software tools to assist identifying and recording critical incident information.

This would have been quite a new departure from the standard CIT format of retrospective reporting. Researchers at IBM in Toronto developed a software system called UCDCam, based on Lotus ScreenCam. This application was used for capturing digitised video of screen sequences during task performance, as part of critical incident reports. In the authors' own words:

We expected the flow of the activities during task performance and reporting to be somewhat structured; in particular, we expected most users will report critical incidents immediately after they occur.

Whereas they discovered quite a delay between the time many users encountered a critical incident and the time they initiated reports. This delay defeated the mechanism for capturing, as context, a video clip of screen activity again stressing the naturally retrospective nature of the approach.

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Copyright EMMUS 1999.
Last updated: September 29, 1999.