It is indisputable that we are living in an era of change and constant technological evolution, which in turn is leading to what we call the information revolution. Every day we have more and more access to information at our fingertips, as well as the opportunity to capture data in enormous quantities.
However, as human beings we have a limited cognitive analytical capacity, that is, our ability to visualize, understand, process and interpret data does not go beyond three or four variables. In this sense, dataviz, the English name for data visualization, is of great help, as it allows us to consume this data in a faster and more understandable way to the human eye, because, without any doubt, a picture is worth a thousand words.
What is a Sankey Diagram?
A very commonly used type of graph, so far in the field of energy technology and thermotechnics, is the Sankey diagramIt is focused on representing flows and their volume relative to the total. A Sankey represents flows by means of “ribbons” whose width is proportional to the volume flowing. It is ideal when you need to answer: Where do my defects come from, through which channel are they concentrated, what part of the total do they represent? Nowadays, this type of graphics is being exported to other fields where it could be useful because of its illustrative nature, such as industrial processes and quality control.
The operation is very visual: it is a type of flow chart in which the width of the arrows is proportional to the amount of flow. These arrows can be combined, split and plotted along the chart depending on the target category.
When to use it in Quality?
- From Pareto To Flow: When the Pareto tells you “what” fails, but you need to see “where” the non-quality flows.
- Compare Levels: Plant → Customer → Measurement Plan → Defect Type.
- Prioritize Actions: Identify bottlenecks or critical foci without losing the overall context.
Practical example
An example of Sankey’s use in industrial Quality Control would be the following:
“I am the quality manager of a large company that manufactures automotive components and I have several plants in Europe; I would like to know which of them collect the highest volume of failures and where they come from, so that I can have a holistic perspective of the situation in my department, and know where I should focus attention during the next quarter. “
The Sankey diagram shows us the volume of failures in our three plants and the flow they follow at 3 levels: by plant, by customer and by measurement plan, which allows us to instantly visualize in which plant we find more difficulties to reach the desired level of quality, which customer projects have the highest number of failures, and in which measurement plans we find more out-of-tolerance parts.
To get the most out of Sankey, three common mistakes should be avoided: Too many Nodes, which saturate the reading-simplify taxonomies and group minor categories; Inconsistent Data, unify catalogs, standardize names and validate before graphing; and No Link To Action, each insight should be translated into a concrete task with a responsible person and date. With these guidelines, the Sankey remains clear, actionable and results-oriented.
