What is the reason why you shouldn't use the 'five times' method to identify the cause of the problem?



Toyota is and has been created 'in order to determine the cause of the problem,' why 'is the cause of the problem, which initially did not appear by repeated five times'll see the' 'five why' method that is, why Why it is also used in a wide range of fields, which is also called analysis . Alan Card, an associate professor of health care research at the University of California, explains problems in applying a method to identify the cause by using five such reasons.

The problem with '5 whys' | BMJ Quality & Safety

Why and why analysis is a problem analysis method that shows the factor 'why' caused by a certain problem and then repeatedly presents the factor 'why' that caused the factor. It is also said that the 'five times why' method is from the claim that by repeating the 'why' about five times, the far cause of the problem that was not seen at the beginning and the countermeasure can be seen.

In the first place, why five such methods have been used to improve the production method of Toyota's automobile factory, but as their usefulness is widely recognized, they have been used in places other than automobile factories. Five reasons are being used for problem analysis in the field of healthcare, such as WHO and the National Health Service (NHS) in the United Kingdom.

Method analysis method with many people who support from the viewpoint that it is very simple method of repeating why why 5 times, and it is convenient to reach the root cause of the problem that was not seen at the beginning. It has been with. However, Mr. Card seems to think that there are problems with using the method five times in the healthcare field.


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Five case studies that are widely used as case studies to explain the method are that five ways were used to find out the “method for preserving the Washington Monument ”. In this case, I use five methods to reach the cause of the problem and the solution of the problem as follows.

◆ Problem:
The state of the Washington Monument is getting worse

why? (1): The condition is getting worse due to the effects of chemicals used to clean the monument
why? (2): The monument is dirty with pigeons and must be cleaned
why? (3): The pigeons are attracted to the spiders that live in the monument
why? (4): The spider is attracted to the clover that lives in the monument
why? (5): Jusrika is attracted to the light that lights up the monument at night

◆ Solution:
Delay the light-up time, and do the light-up later than at the most gathering sunset

It is difficult to identify from the apparent state that 'the state of the Washington Monument is getting worse' that 'the cause is that the light is attracting Yusrika.' Seems to be used very well.

However, the reason why five methods were actually applied was the Lincoln Memorial , not the Washington Monument, and the direct cause of the deterioration was not the chemical but the water used for washing. Also, the memorial hall was not soiled by the pigeon's houn attracted by the spider, but was merely soiled by eggs and remnants that Jusrika was drawn into the light and collided with the memorial hall.

Certainly, the measures against extermination of Jusrika were effective in the case of Lincoln Memorial Hall, but actually delayed the light-up at night, and had an unexpected negative effect. Although the number of firewood decreased by 85% by delaying the light-up, dissatisfaction from tourists who visited to take photographs of the Lincoln Memorial continued. After all, it was said that I had to restore the light up time.

The case that is widely used as a model case in which the 5 methods have worked well highlights the problems such as wide stakes that can not be seen with the 5 methods, and errors in the logic process up to the solution. Card pointed out that it was something that We can see that there are five cases why the method does not work well for problems involving complex factors, as well as simple ones.

Also, although the purpose of the five-why method is to identify a single cause for a problem, the path from problem to cause is often not one. For example, when examining the case that 'the wrong patient has been dosed', suppose that the cause was identified using five reasons as follows.

◆ Problem:
I have been dosed to the wrong patient

why? (1): Did not check the wristband identifying the patient
why? (2): There was no wristband
why? (3): The printer for printing on the wristband was broken
why? (4): The label was stuck in the printer
why? (5): There is a problem with the printer design

However, in reality, it is possible to repeat a completely different 'why' from the problem that 'the wrong patient has been dosed'. Card pointed out that in this case the cause found in the five methods is likely to be only one of a wide variety of causes. Problem solving that relies on the 5 times method may sometimes overlook important causes. In real problem analysis, there are many possible causes as shown in the image below.

5 times why Why the method is repeated 5 times to find out the far cause of the problem. However, the most important cause may be further away, or it may be in close proximity that does not need to be repeated five times, which is not applicable to all problems. In addition, there is no guarantee that there is only one cause, and there may be a solution that can not be understood from the investigation of the cause, such as 'introducing a device or system that solves all new' instead of searching for the cause. Mr. Card says.

Card points out that it is an advantage that it is easy to take action to simplify the problem-solving process where why the method looks complicated five times and to think deeply about the cause of the problem. On the other hand, 5 times why using the method often does not notice the essence of the problem, and 5 times in areas such as healthcare where the process is not streamlined and simplified environment like car factory I conclude that I should not use the method.

in Note, Posted by log1h_ik