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In general, 4Ms is not a new concept or invention but I found many definitions on it and different ways people apply its in practice. For example the definition of 4Ms:

  • “The proposed 4M approach takes into account all the most important aspects involved in the manual assembly: Method, Machine, Man and Material. The final goal is to provide a means for the concurrent improvement of the product design, the work-station ergonomics, and the assembly tasks.”
  • or 4Ms represents factors (reasons) which influence on quality coefficient of the final result of the concerned process.
  • or The 4Ms is used to name categories of potential root causes on the Ishikawa diagram.
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This method has been used for a long time, especially in the root cause analysis (fish-bone diagram, Ishikawa diagram, herringbone diagrams, cause-and-effect diagrams, etc., ) and I believe that in manufacturing environment, people are very friendly with how to apply this method on production control, production improvement, overall efficiency measurement, process design, etc.,

However, my observation in other industries such as service, healthcare, etc., even in non – production function/departments of a manufacturer, 4Ms is not well-understood and applied effective. So my objective in this article is to summarize the methodology of 4Ms and introduce a little bit about my approach to apply it in practice.

So What is 4Ms?

4Ms represents the most important factors which influence on the final result of any concerned process.

Figure 1 -The most popular cause-and-effect diagram with categories by 4Ms

For a long time using the 4Ms method, not only for root cause analysis (cause-and-effect) but also for many purposes, I modify a little bit on this method and connect it to the IPO (Input – Process – Output) model. Of course we can add the S & C to have a full SIPOC, but simply I just used the IPO. The first M (Material) is corresponding to the I (Input), the three other Ms (Man, Machine, Method) are components of the P (Process), and the O (Output) represent not only for the effect, but also for every results we can get from the concerned process.

Figure 2 – a proposal model combine of 4M and IPO

So where/when/what can we apply 4Ms and IPO methods?

In a basic, 4Ms method and IPO model could be applied for any situation, purpose, anywhere and every time. Both methods give us a total systematic point of view in practice and help us to prevent missing any important factor which is able to influence to the Output or final results. Obviously, we can expand this model by putting it in a specific environment or situation, and our model will be changed as figure 3.

Figure 3 – a proposal model combine of 4M and IPO in a specific environment or situation

Mathematically, this model is able to explain by an y = f(x) formula:

Output = f(Process, Input, specific environment or situation)

For example, if the Output is productivity, we can explain this model in below formula:

Productivity = f(Process, Input, specific environment or situation)

This is high-level, we can be more specific by deep dive into each factor:

Productivity = f(Man, Machine, Method, Material, Environment, specific situation…)

If this is simply a linear model, we can represent this formula to:

Productivity = a1 x Man + a2 x Machine + a3 x Method + a4 x Material + a5 x Environment + a6 x specific situation + b1(Man x Machine) + b2 (Man x Method) + b3 (Machine x Method) + …


This formula can explain for the model in figure 3.

I will give an example to explain its application in practice:

In an assembly production line: look at the figure 4, this is a simple physically manufacturing process. The operators performed assembly process by putting the small part to the wheel. If you want to improve this process or the quality of final product, how 4M help you?

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Figure 4 Ford’s assembly line in 1913

You know that the Ouput (final product or productivity of this process) and its expectation (quality meet customer specification) is influenced by the operators (Man) and their individual assembling skills, the conveyors surface, supporting tools (Machine), the standard operating procedure (Process), quality of the materials, etc.,

Figure 5Group to different categories

So if you want to improve the quality of the final products, what factors can you improve? Where is your start? You can start at any categories Man, Machine, Material, Method. But if you improve only one factor Man, or Machine, or Material, or Method, how much improvement you can get? And what if you analyze the with-in influence of each factor and interaction between all factors to the Output (or final results), the solution come up as the results of your analysis, how much improvement you can get?


The idea of 4M & IPO model is simply give you a systematical and total point of view on what individual factor as well as what factor-to-factor interaction able to influence on the expected Output (or final results).

In many situation, companies which their manufacturing process have primarily machine or automate equipment, tend to narrow their focus on the machine and underestimate impact of factor Man. Their continuous improvement framework focus on improve the equipment efficiency as much as possible. In a meanwhile, companies which their manufacturing depend on operator’s skills tend to narrow their focus on the people productivity, and lack of focus on the potential of the machine and technology.

By the same approach, you can do the 4M analysis and improvement in any process of any industries.

Figure 6 –Man, Machine, Method in the service environment

Discussion: But is 4Ms only for process improvement?

Not yet. Of course 4Ms is a powerful method for process improvement, but it’s also the most important method you should apply during the process design and/or product design phase, and in daily operation management.

From my experience, many improvement projects or investment project on new process and/or new products lack of a 4Ms review and design. The obviously effect of this missing is the final solution not to work or fit-to-spec or purpose, and additional budget required to fix for the lack-of-4Ms review and design. A lot of over-processing and over-budget due to lack of 4Ms review and design.

Absolutely, the 4Ms technique is able to apply in any phase of a process from the concept to design phase, from prototype to mass production, from daily control to continuous improvement, innovation, etc.,.

By understanding and using it effective, you can add much valuable in your continuous improvement activities.

Chapter 4ms. MaI personally consider 4M & 1E as the 'friendly basic compass' to structurally guide program managers. They are the main topic to be considered before a program manager can work on the details of matters in a structural manner.A program manager can group each matter into these 5 categories, before working on the details. This helps the program manager to plan better, and utilize his/her limited resources more efficiently & effectively.4M:a. Man: All human resources related matter such as direct labor & indirect labor, hiring & firing, training, wages & benefits, knowledge & experiences, etc should roll under this category.b. Machine: Anything related to equipments, testers, jigs, fixtures, calibrations, specifications of the machine, templates, pallets, tables & chairs, tools, etc. c. Method: Any methods, instructions, specifications, guide, tolerance, etc. d. Material: This applies to both direct & indirect materials. Direct materials are the list of materials that is listed in the BoM (Bill of Material). They can be easily counted. Indirect materials are materials that are not listed in the BoM (Bill of Material). Alternatively, they can be items that are difficult to count. For example the materials that are in liquid, semi-solid and powdery form.1Ee. Environment: This applies to work station, temperature, ESD (Electro-Static Sensitive Device), moisture sensitive devices, air conditioned, humidity, vibration, air pressure, clean room environment, dust free requirement, etc. This is a rather small portion, but anything that is related to environment will fall under this category.

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If you would like to know more on a basic 4M + 1E checklist, please write to me. I hope the templates that I have can minimize your efforts to re-invent the wheel.
Updates on Aug 30 2020:
I have written more information on the topic of 4M & 1E that provides more details.
Please click on the below link to get to this article: