‘The Problem with…’ series covers controversial topics related to efforts to improve healthcare quality, including widely recommended but deceptively difficult strategies for improvement and pervasive problems that seem to resist solution.

This quote also makes the case for the technique's simplicity. Asking ‘why’ five times allows users to arrive at a single root cause that might not have been obvious at the outset. It may also inspire a single solution to address that root cause (though it is not clear that the ‘1H’ side of the equation has been adopted as widely).

In terms of pedigree, ‘5 whys’ traces its roots back to the Toyota Production System (TPS). 9 It also plays a key role in Lean 10 (a generic version of TPS) as well as Six Sigma, 11 another popular quality improvement (QI) methodology. Taiichi Ohno describes ‘5 whys’ as central to the TPS methodology: The basis of Toyota's scientific approach is to ask why five times whenever we find a problem … By repeating why five times, the nature of the problem as well as its solution becomes clear. The solution, or the how-to, is designated as ‘1H.’ Thus, ‘Five whys equal one how’ (5W=1H). (ref. 9 , p. 123)

The ‘5 whys’ technique is one of the most widely taught approaches to root-cause analysis (RCA) in healthcare. Its use is promoted by the WHO, 1 the English National Health Service, 2 the Institute for Healthcare Improvement, 3 the Joint Commission 4 and many other organisations in the field of healthcare quality and safety. Like most such tools, though, its popularity is not the result of any evidence that it is effective. 5–8 Instead, it probably owes its place in the curriculum and practice of RCA to a combination of pedigree, simplicity and pedagogy.

The logic of the solution was sound, as far as it went. But it was predicated on an incomplete understanding of the broader system, its stakeholders and the purpose of the monument itself. If anything, this window on the complexity of real-world problem solving adds to the value of this teaching example. If the first ‘aha moment’ is followed by this second one, trainees will not only learn that distal causes can have unexpected outcomes, but also that systems thinking requires both depth and breadth of analysis.

However, the most important problem with this example is that, while the solution was ‘effective’ in one sense, it still failed: Messersmith [the consultant entomologist who worked on this project] thought that because the insects swarmed only at sunset, a one-hour delay in turning on the monument lights would go far in solving the problem. The technique worked, reducing the number of midges in the monuments by about 85 percent. ‘But tourists who had driven hundreds of miles to have their photographs taken at the monuments were not happy,’ he said. ‘They complained every day, and the lights went back on.’ 16

The first ‘why’ could just as easily have tackled other causes, such as rain or acid rain (a significant concern at the time), rising damp, erosion from windborne particles or damage from freeze-thaw cycles. 15 Or, if the goal had been to prevent harm to future monuments, the first ‘why’ could have focused on the use of marble as a building material, the choice of building site, etc.

But that only speaks to the details that were described. The analysis is also incomplete in a number of more important ways. For instance, it only addresses one potential source of deterioration: cleaning water.

In terms of the story's details, the monument is question was actually the Lincoln Memorial, and it was not being damaged by the use of harsh chemicals. The real culprit was simply water. Pigeons were not an issue at all, and while there were ‘tiny spiders’ (ref. 14 , p. 8) at the memorial, they were not a major problem. Instead, most of the cleaning was necessary because swarms of midges were dazzled by the lights and flew at high speed into the walls of the memorial, leaving it splattered with bits of the insects and their eggs. 12 , 14

Joel Gross 12 investigated the foundation of this example and discovered that many of the details are incorrect. And, crucially, the broader story it tells is incomplete.

This is a great teaching example because the ‘root cause’ is so unintuitive. Who would think, before exploring the issue in depth, that lighting choices could endanger a marble monument? But, as is so often the case, reality is messier than this simple illustration.

Why? Midges are attracted by the fact that the monument is first to be lit at night.

Possibly the most famous ‘5 whys’ case study to be used in this way focuses on efforts to preserve the Washington Monument. 12 , 13 Details vary slightly depending on the source, but it usually looks something like this:

The pedagogical argument for ‘5 whys’ is that it creates an ‘aha moment’ by revealing the hidden influence of a distant cause, which illustrates the importance of digging deeper into a causal pathway. This quick and easy learning experience can be a powerful lesson in systems safety and QI.

The problem with ‘5 whys’ in RCA

‘5 whys’ has been the subject of a number of caveats and critiques. For instance, Minoura, one of Ohno's successors at Toyota, highlights the potential for users to rely on off-the-cuff deduction, rather than situated observation when developing answers, as well as difficulty in prioritising causes, if multiple ‘5 whys’ are used.17 Mark Graban, a thought leader in the Lean community, points out that ‘5 whys’ is just one component of what should be a far more comprehensive problem-solving process.18 And Serrat clarifies that users should not feel constrained by the arbitrary number in the tool's title: more, or fewer, than five ‘whys’ may be required.19

But the real problem with ‘5 whys’ is not how it is used in RCA, but rather that it so grossly oversimplifies the process of problem exploration that it should not be used at all. It forces users down a single analytical pathway for any given problem,13 insists on a single root cause as the target for solutions9 ,13 ,20 and assumes that the most distal link on the causal pathway (the fifth ‘why’) is inherently the most effective and efficient place to intervene.

A single causal pathway A credible ‘5 whys’ approach to a wrong patient medication error might look like this (adapted from Battles et al):21 Incident : Wrong patient medication error Why? Wristband not checked Why? Wristband missing Why? Wristband printer on the unit was broken Why? Label jam Why? Poor product design

But another team could easily come up with five wholly different and equally valid ‘whys’. And any single string of ‘5 whys’ can provide only a blinkered view of the complex causal pathway that led to the incident. This is illustrated by figure 1, a causal tree diagram (or, more accurately, a ‘causal and contributing factors tree diagram’) depicting the underlying issues that gave rise to the adverse event. Figure 1 A causal event tree (adapted from ref. 21). ID, identification; IT, information technology. It is clear from the tree diagram that the causal pathway related to the wristband printer is neither the only relevant cause of the incident nor indisputably the most important. A serious effort to solve the myriad problems that gave rise to this incident would have to tackle a number of other causal pathways as well. These might include pathways related to a maladaptive workplace culture,22–25 clinical and information technology (IT) staffing, orientation of agency staff and the absence of a forcing function26 to ensure that patients are properly identified before medication is administered. It could also include a focus on improved infection control and better preparedness for infectious disease outbreaks. Solutions based on the ‘5 whys’ in the example above would leave all of these issues unaddressed. There is also no objective or reliable means of mapping out the causal pathway, which is a critical failing when only one pathway will be examined. Consider the variant below, which follows essentially the same causal reasoning as the first example: Incident : Wrong patient medication error Why? Wristband missing Why? Wristband printer on the unit was broken Why? Healthcare system purchased an unreliable printer Why? Poor process for evaluating and purchasing ‘non-clinical’ equipment Why? Equipment deemed ‘non-clinical’ is not seen as safety-critical

This version skips the step of asking why the wristband was not checked and moves directly to asking why it was not there. It also sticks to the high-level issue of the printer being broken, without delving into the details of the label jam. ‘Skipping’ these questions allows the analysis to go deeper because it leaves more ‘whys’ available. This example also maintains a focus on issues within the organisation, rather than the design of the printer. This would lead to very different solutions. But because this approach skips past the question of why the wristband was not checked, it closes the door to questions about other reasons why it was not checked. In figure 1, this would include the lack of a forcing function. But in another scenario, it might include a desire to avoid waking the patient;27 an unreadable wristband (eg, smudged, crinkled or occluded);28 the lack of a label on the medication;29 confusion caused by multiple wristbands;30 lack of trust in the wristband data due to frequent errors31 or any of a number of other causes.28–31 Users could also go down an entirely different causal pathway. An equally reasonable ‘5 whys’ for this incident could look like this: Incident : Wrong patient medication error Why? Patients with similar names in the same room Why? Not feasible to try ‘juggling beds’ Why? Not enough nurses to deal with the influx of patients Why? Nurses affected by an outbreak of norovirus Why? Poor adherence to time-consuming infection control interventions Why? A culture of ‘just get the job done’

There are many ‘correct’ ways a team might use ‘5 whys’ to assess even this one incident. And it is unlikely that any two teams would independently arrive at exactly the same results. This subjectivity is critically important because ‘5 whys’ focuses on only one root cause at the end of one causal pathway. More sophisticated practice in the use of ‘5 whys’ might produce two causal pathways, focusing on the main service failures uncovered, rather than the event itself (ie, a set of ‘5 whys’ for ‘wristband not checked’ and another for ‘verbal identification failure’). But this is not how use of the tool has generally been taught in the healthcare industry.1 ,3 ,32 And even this unusually thorough approach would identify only 2 of the 30 causal pathways shown in the tree diagram.

A single root cause Forcing users down a single causal pathway should be disqualifying by itself. But ‘5 whys’ narrows the scope for improvement even further by insisting that risk control efforts must focus on a single root cause for each causal pathway. In the first healthcare example above, for instance, the root cause would be ‘poor product design’, and this would serve as the sole target for improvement efforts. But accidents are seldom the result of a single root cause.33 So focusing exclusively on one (or even a few) arbitrarily determined ‘root causes’ is not a reliable method for driving improvement—especially in a system as complex as healthcare. As Wieman and Wieman wrote: “Unfortunately … restricting the number of variables [considered] in a complex system only results in an increased potential for errors of omission” (ref. 34, p. 117). How much might be omitted when using ‘5 whys’? The tree diagram for our example uncovers more than 75 whys (causes and contributing factors), each of which is a potential target for action to reduce the risk of a recurrence. The ‘5 whys’ approach would identify only one (or possibly two) root cause as target for action. At best, this represents <3% of the opportunities for improvement identified using the tree diagram.