How to use a fishbone diagram

Showing branched causality between problem antecedents and an identified effect.

Figure 1. Fish skeleton, showing branched casuality between problem antecedents (skeleton ribs) and an identified effect (fish head)
Figure 1. Fish skeleton, showing branched casuality between problem antecedents (skeleton ribs) and an identified effect (fish head)
Starting with a glib problem statement that is imprecise, tacitly psychologically encourages the participants in the room to frame their thoughts around that (poorly-written) problem statement. This creates the danger of groupthink.

A well-specified Problem Statement

Many fishbone diagrams have failed because of an overly condensed, imprecisely defined problem statement. It should be replete with correlative data and information to the best of the investigating team's knowledge at the start of the project. So instead of:

Leak identified on bioreactor
Prefer something like this:
… at 12:18 on 15Oct18 a leak was identified by [name] on the nth supplement port of manifold 3B during the inoculation procedure (BR-0038).

This makes it clear:

  1. how far into the inoculation it occurred
    (e.g., 12 minutes into the process, which may point in a different causal direction than if it happened immediately upon opening an additive valve)
  2. which personnel and shift were involved
    (to be able to gather immediate real-time information relevant to the activities of the process)
  3. how often there have been issues with this process step in this particular batch record
  4. whether this particular piece of equipment (supplement port) has been implicated in other similar issues in the past

The investigators should be brainstorming with experts in a co-located space. Presumably everyone is looking at the board/flipchart together. The focus should be on evidence-based knowledge (EBM) techniques.

The Fishbone Diagram

There isn't one flavour of a fishbone diagram that suits all organizations.

6M Categories

The most comprehensive and simple version. Consists of Man, Material, Method, Measurement, Machine, and Mother Nature.
Using only four or five Ms does not provide good resolution into multifactorial issues!
Figure 2. 6M Categories
Figure 2. 6M Categories

Fishbone By Process Step

This format uses the subordinate steps within a process to frame the categories that help the investigators exhaustively identify causal factors. Look at each step and ask: What happens during step 2 of the process that could have allowed this effect to occur?
Figure 3. Fishbone By Process Step
Figure 3. Fishbone By Process Step
Fishbone By Process Step: Begin by taking out the SOP, and flip to the section that has a process map in it (Figure 4) and build the fishbone diagram from there in a stepwise fashion.
Figure 4. Process Map swim lanes
Figure 4. Process Map <q>swim lanes</q>

In Conclusion

Used consistenly and frequently, the fishbone didagram can help you identify root causes of issues (not just causal factors) and develop CAPAS to eliminate those problems.

References

  1. Locwin B. When to use a fishbone diagram — and why you should do it more often than you think www.pharmaceuticalonline.com/doc/…
  2. Card AJ. The problem with 5 whys BMJ Qual Saf 2017;26:671-677.
  3. Anderson S. Discovering Four Types of Fishbone Diagrams blog.minitab.com 06 April, 2020
  4. The Ultimate Guide to Fishbone Diagrams (Ishikawa / Cause and Effect) creately.com 3 February, 2021.
  5. The Ultimate Guide to the Fishbone Diagram leanopedia.com 11 March, 2020.