What’s in a name: PDSA or PDCA?

Image by Pete Linforth from Pixabay

Whilst learning Toyota Kata and training new improvers over the past few months, I have been asked a few times ‘what is the difference between PDSA and PDCA?’, and does it matter?*

To be honest I’m quite laid back about it, because to me, it is the experimenting and learning from the experiments that matters to me, rather than the words and the acronyms. Particularly since the evidence (Reed and Card, 2016) is that there is little fidelity in the use of PDSA regardless of its name variants. And I suppose because I don’t really have a view, as to me, it is rather a bit of an improvement geek terminological recurring argument, rather like the recurrent argument about which improvement ‘brand’ is the best. So I thought I would explore it a little bit in this blog, because there are quite a few stories and some evidence about this (and I have probably missed some).

PDCA stands for ‘Plan Do Check Act’. Apparently developed in Japan by the Japanese Union of Scientists and Engineers (JUSE), (some suggest Dr. Ishikawa, of fishbone fame, in particular had a big role in this), during the early 1950s as their interpretation of the knowledge shared by Dr Deming during his visits to Japan (Martin, 2012. The outstanding organisation). Moen (undated) reports that this was an interpretation of previous traditional quality control processes in manufacturing, known as the Shewhart Cycle or Deming Wheel. That is… ‘design (specify), make, inspect/(sell)’. With an addition of ‘re-design (or do market research)’ at the end, based on what had been learnt. This in itself is reported to be an extension of the deductive scientific method: Hypothesis-test-evaluate. In that process, experimenters (if my epistemological memory of Popper is accurate), try to design experiments that will disprove a hypothesis, with a sceptical perspective. Thus, as attempts to disprove a theory overtime increasingly fail, this makes theories stronger as it becomes more difficult to find new ways of refuting the hypothesis, therefore the theory is more likely to be the ‘truth’. (There are many counterclaims and epistemological alternatives and critiques of this view of truth).

Deming argued that PDCA needs changing to a PDSA because the word ‘check’ in Japanese did not translate well into English, and it was being corrupted. He argued that ‘check’ seemed in the Western hemisphere to be interpreted in a way not always conducive to learning, but more ‘confirmation if the plan was met’ or otherwise, that is: compliance. Hardly the scientific scepticism desired to design and conduct experiments. Instead, Deming advocated changing the ‘check’ to ‘study’, and distanced himself from PDCA. Hence PDSA, the Shewhart cycle for learning and improvement (Deming, 2000. The New Economics, 2nd Ed). Given that the history of the development of PDSA indicates that it is an iteration developed from a model incorporating inspection, I’m not overly surprised that ‘check’ can be interpreted as a possible form of compliance. In addition, in American English, a ‘check’ is a ‘tick’, as in, when your homework is marked is it ‘right or wrong’. An undercurrent of compliance, inspection and assurance within the cycle. (Other stories as to the difference include ‘PDCA is the American version of PDSA’ and that ‘PDCA is used in manufacturing, whereas PDSA is used in healthcare’ although I can’t substantiate either of these so I strongly suspect them to be false). I have also seen the C described as ‘Consider’, which is, a little closer to ‘Study’ in meaning, imho.

The letters C and S in the improvement cycle are not the only variants however.

The Improvement Guide (Langley et al. 2009) refers to PDSA as ‘Plan Do Study Act‘, but Imai, in his seminal book ‘Kaizen’ (1991) refers to a slight variation on this: ‘Plan Do Study Action‘ and it is also known as as ‘Plan Do Study Adjust‘ (I can’t find a source, if you know of one, please let me know) or even ‘Plan Do Study Adjust (Adopt, Adapt or Abandon)’ So does that difference in ‘A’ matter as much or as little as the C/S variation? It seems to be discussed less, perhaps it is less contensious.

Imai (1991) also seems to criticise the West for some of their interpretation of PDCA but he focused on the A, rather than the C. He suggests that ‘Act’, is interpreted by the West as more like fire fighting. Referring derogatorily to the West’s interpretation and execution of the cycle as ‘PDCF’: ‘Plan Do Check Fire-fight’, rather than learning and adjusting, also suggesting that the West seems to view goals and objectives as fixed and are either met or not, rather than continually improved upon. A continuation of the undercurrent of compliance, i.e. it didn’t meet the check, so fix it, become compliant. I also wonder if ‘Act’ sounds a bit ‘Big Bang’. Do a small test, check if it worked then go for it and implement, rather than ‘so what actually happened and what did we learn from that experiment, did we move our threshold of knowledge, what do we need to adjust and change next?’ Reflecting, learning and adjusting, not just acting.

Photo tweeted by Tracey Richardson, former Toyota Sensei on 5/6/19; @tracey_san

Further, Imai and others (see photo) indicate the importance of small experiments, one after another, and ensuring that ‘SDCA – standardise, do, check, action’, before starting PDSA, to ensure current standards and goals are set and stabilised before using PDSA to try to improve upon them (the role of the challenge and target conditions in Toyota Kata imho). This stage is often missed in my view in healthcare improvement, and can be confused with target setting, instead of standard setting, perhaps mimicking the same interpretation and execution problem as ‘Check’ and ‘Study’, as ‘targets’ are so often externally driven by regulatory agencies and other third parties.

But at the end of the day, does it really matter? I have no doubt that as research into improvement continues there will continue to be new versions of PDSA with new acronyms and new variants of words, each time trying to improve upon the previous iteration of the model. This is how knowledge gradually develops, it is arguably what improvement is about. The point for me is less the words and the letters, and who said them first, but more about the understanding underpinning PDSA’s use, who is using it, why and how, and how can we keep developing our knowledge and use of these cycles. Checking, Inspecting, Studying, Acting, Actioning, Fire Fighting and Adjusting. All useful in some circumstances, probably. I do wonder though, if the debate about these letters is still in some way a recurrence of the somewhat flawed ‘inspection-bad‘ and ‘improvement-good’ argument, which I have previously suggested may not be a very helpful dichotomy, as imho they are inherently connected and there is much shared purpose.

For me, improvement is more about understanding where are trying to go, where we are now in relation to that, working out what we don’t know that is stopping us getting there and trying stuff out to see what we can learn on the way there. I would rather that we can hear about all the letters and words, and different variants and learn about each and make up our own views critically, as to which to use and if it matters. I mean we could have PDSAAA or something else, to try and get around the tendencies to not use it as intended and see if changing the letters or the words make a difference. Or we could just practice and get better at applying the principles that underpin it. The research (Reed and Card, 2016) suggests that improvers in healthcare are not good at applying PDSA, and rarely get beyond P and D, never mind the last two letters (of whatever cycle variant). Whilst academically, the terms may need to be precise; but imho, I don’t think pragmatically, that ‘we improvers’ in practice need to be quite so purist about it. Perhaps focussing our efforts on learning how to improve, ensuring we are understanding and reflecting on what actually happened and learning, adjusting and acting based on that, after each experiment is more important. Rather than arguing or worrying what words and letters we should use. I feel this would be a more valuable use of our time and help us to be more effective in how we improve in health and care.

* for simplicity in this blog, I will use PDSA as the phrase in the text to refer to the 4 steps with many terminological differences

Addendum: since first writing this I have also come across.. CPDnA. … which stands for Check (does it meet the standard), Plan (what to do if not), Do, (n… as many times as needed till it does) and then A (set new standard if now better). Seems more like hold the standard to me, by putting in countermeasures than step changing the standard, but maybe I’m just being picky.



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