9.2 Cause and Effect Analysis

Also known as the Ishikawa Diagram or the Fishbone Diagram for Process Failure, this method encourages the investigation to follow a structured process of identifying contributing factors and risks. The technique uses a diagram-based approach for thinking through all of the possible causes of a problem.
It can be summarized in the following steps and on the corresponding diagram below:

  1. Identification of the problem - what has occurred to imply risk (what has gone wrong?)?
  2. Identification of the factors that could contribute to causing the problem (systems? equipment? personnel? external factors? etc.)
  3. Identify possible causes for each factor
  4. Analyse the diagram and decide on further actions to test the different potential causes (data analysis? survey? interview? research?)

Table 2. ‘Five whys’ Examples why was the wrong virology report recorded?

Why was the wrong virology report recorded? It was a human error – the technician saw the reactive result but ticked the ‘non-reactive’ box on the results form
Why did the technician make a mistake like this? He was not used to manually recording results and was carrying out a number of tests simultaneously
Why was he manually recording results if he was not used to doing that? The automated testing system is used during the normal busy day but not at night when the number
of tests required is too low to justify the cost
Why was he not used to the night time procedure? It was his first time working alone at night and he had not used the manual procedure for a number of years
Why was he carrying out a procedure for which his competence had not been checked? The person who normally worked at nights was ill
Root Cause The technician was carrying out a task for which he had not been adequately trained and supervised.


Table 3. ‘Five Whys’ Examples Why was the bone packaging torn when it was received in the operating theatre?

Why was the bone packaging torn when it was received in the operating theatre? The cortical bone strut inside was sharp and tore the material
Why was material used for packaging that was susceptible to tearing by sharp bone? It had always been used by the tissue bank for all their previous products
Why had this problem not been seen when the packaging was validated? The validation was carried out only for ground bone products which did not have sharp points
Why was the packaging material not validated for this new product? The validation already in place for ground bone was considered adequate
Why was this new risk not identified as a reason for validation of the packaging for cortical struts? No risk assessment was carried out when this new product was introduced
Root Cause Lack of a risk assessment when a product change was being introduced.