CREAM (1998)

CREAM - Cognitive Reliability and Error Analysis Method

The text below is a general introduction to CREAM, written about 2002-3. The views expressed were reasonable at the time, but an important disclaimer has been added (at the bottom of this page).

Human work can be characterised by a scale going from "doing" to "thinking". Some tasks, such as manual skills and following a procedure, require much "doing" and little "thinking", while others, such as diagnosis, planning, and problem solving, require much "thinking" and little "doing". The development of modern technology has changed the nature of human work from being mostly manual skills to being mostly knowledge intensive functions (usually referred to as cognitive tasks). In present-day industrial environments the amount of "thinking" is increased while the amount of " doing" is reduced. This state of affairs has consequences for both system design and reliability analysis. In system design, for instance, conventional ergonomic aspects must be replaced by cognitive ergonomics. Similarly, in risk assessment and reliability analysis, first generation Human Reliability Analysis (HRA) must be replaced by a second generation, context-dependent cognitive reliability analysis.

CREAM (Cognitive Reliability and Error Analysis Method) is a specific proposal for a second generation HRA. CREAM will enable an analyst to achieve the following:

  1. Identify those parts of the work, as tasks or actions, that require or depend on human cognition, and which therefore may be affected by variations in cognitive reliability,
  2. Determine the conditions under which the reliability of cognition may be reduced, and where therefore these tasks or actions may constitute a source of risk,
  3. Provide an appraisal of the consequences of human performance on system safety which can be used in a PRA/PSA, and
  4. Develop and specify modifications that improve these conditions, hence serve to increase the reliability of cognition and reduce the risk.

Steps 1 - 3 are the core of CREAM. Step 4 serves the purpose of ensuring that the proper conclusions are drawn from the analysis, and that the necessary changes to the system are correctly specified.

CREAM can be used in several different ways:

  • as a stand-alone analysis method, for either retrospective or prospective analyses, using a consistent taxonomy for error modes and error causes.
  • as part of a larger design method for complex, interactive systems
  • as an HRA in the context of an Integrated Safety Analysis (ISA) or Probabilistic Safety Analysis (PSA).

CREAM provides the core functionality of these services, i.e., the concepts, the classification system, the cognitive models, and the methods. In order to be properly used it is necessary to supplement with application or plant specific information, e.g. in the form of values for specific performance parameters, detailed operational and process knowledge that defines the context, etc. CREAM has been developed as a written guideline supported by a hypertext tool. A full description can be found in the book "Cognitive Reliability and Error Analysis Method".

A specialised version of CREAM for use in the analysis of traffic accidents has been developed as part of the FICA project. The adapted version was named DREAM, for Driver Reliability and Error Analysis Method. Later, a version was developed for use in maritime accident analysis. It was appropriately named BREAM - B for the ship's 's Bridge.

Disclaimer (written 2012, updated 2021)

Although CREAM still appears to be used and referenced, it is only fair to point out that the method from my point of view is obsolete. There are several reasons for that. First, because it focuses on how actions can fail or go wrong, rather than on the variability of performance, i.e., a Safety-I perspective (q.v.). Second, because it focuses on one part or 'component' of the system only, namely the human(s) - and even more narrowly on human cognition. While this seemed sensible in the aftermath of the debates around first and second generation HRA, it can now be seen as representing a structural rather than a functional viewpoint. Third, because it indirectly lends support to the concept of 'error'. (It doesn't really, of course, but no one seems to have noticed that.)

Seen in hindsight, only the A (for Analysis) and M (for Method) make sense. Cognitive Reliability (the 'CR') is a misleading oversimplification: explaining human performance as based on 'cognitive processes' represents a myopic information processing view, and talking about the reliability of such processes is an artefact of the PRA/PSA mindset. 'Error' is, of course, theoretically vacuous as explained elsewhere. (Not that this has any effect on its popularity.)

Bottom line: CREAM seemed to be a good idea at the time, but isn't any longer. Sic transit ...