The Role of Control Charts and Fishbone Diagrams in Six Sigma


The importance of efficiency and quality cannot be overstated. Organisations try to reduce faults, enhance processes, and optimise performance to obtain a competitive advantage. This quest for perfection has developed many approaches and technologies, including Six Sigma Certification. Six Sigma strives for near-perfect quality by detecting and eliminating process faults. Six Sigma Tools are critical to its effectiveness, and two of the most important are Control Charts and Fishbone Diagrams. These tools are crucial components of the Six Sigma technique, allowing organisations to make educated decisions, improve processes, and ultimately offer superior goods and services.

The Essence of Six Sigma  

Before getting into the intricacies of Control Charts and Fishbone Diagrams, it’s critical to grasp Six Sigma’s key principles. Six Sigma, developed by Motorola in the 1980s and popularised by firms such as General Electric, is a data-driven methodology that aims to reduce process variability, resulting in fewer faults and higher quality. The ultimate aim of Six Sigma is to attain a level of performance in which the number of defects is statistically negligible, equal to just 3.4 faults per million chances.  

Harnessing Six Sigma Tools  

Six Sigma, the well-known process improvement and quality enhancement approach, is supported by a complete set of tools for diagnosing, analysing, and correcting process inefficiencies. Control charts and Fishbone diagrams stand out as crucial foundations among these tools. When used properly, these technologies help organisations negotiate the complicated landscape of process variability and causation, eventually propelling them to operational excellence.  

Understanding and controlling process variability is critical in the field of process improvement. Control charts thrive in this situation. These charts, created in the 1920s by Walter Shewhart and modified by successive practitioners, visually represent process data across time. Control Charts provide information by showing data points and setting upper and lower control boundaries.  

Control Charts  

Control charts are visual representations of process data across time. They are also known as Shewhart charts or process-behavior charts. They enable organisations to monitor process stability and predictability. Control charts are handy for spotting deviations that may lead to faults. By analysing the data presented on these charts, organisations can discern between common cause variation (inherent to the process) and unique cause variation (due to external causes). This distinction is critical because, although common cause variation may be handled by improving the process itself, special cause variation necessitates identifying and eliminating external influences.  

The primary types of Control Charts used in Six Sigma are:  

  1. X-Bar and R Chart: This chart monitors a process’s central tendency and dispersion. The X-Bar chart displays the sample’s average, whereas the R-chart displays the sample’s range.  
  1. Individuals (I-MR) Chart: This chart is utilised when data is gathered one at a time rather than in groups or batches. It is helpful for monitoring processes with tiny sample numbers.  
  1. P Chart: The P chart is used for processes that involve proportions or percentages, such as defect or error rates.  
  1. NP Chart: The NP chart, which is used just for non-defective objects, is used to monitor operations utilising count data, much like the P chart.  
  1. C Chart: The C chart is employed when counting the number of defects in a constant-size sample.  
  1. U Chart: This chart tracks the average number of faults per unit in processes with variable sample sizes.  

Control charts assist organisations in making educated judgements regarding process improvement projects. They provide for timely actions by alerting users when a process deviates from its intended behaviour. This guarantees that corrective measures are implemented as soon as possible, preventing faults and maintaining the required level of quality.  

Fishbone Diagrams  

Fishbone diagrams, also known as Ishikawa diagrams or cause-and-effect diagrams, are visual tools used to discover and analyse the reasons for a problem or quality issue. The diagram’s name comes from its design, which resembles a fish skeleton with a primary spine (the issue statement) and branches (the likely causes). Fishbone Diagrams are helpful for analysing complicated situations and comprehending the links among many contributing components.  

The graphic is divided into numerous categories that may be customised to match the specific topic. These categories frequently include:  

  1. Man: Human resource factors such as skills, training, and workload.  
  1. Machine: Aspects of the process’s equipment, technology, and tools.  
  1. Method: Process-related factors such as processes, protocols, and workflow.  
  1. Material: Aspects about the materials or inputs employed in the process.  
  1. Measurement: Elements about the techniques used for measurement and data collecting.  

Organisations may find fundamental causes of issues and make targeted improvements by rigorously identifying and analysing probable reasons within each category. Fishbone Diagrams help cross-functional cooperation by bringing together stakeholders from many departments to develop and validate potential causes.  

Synergy in Six Sigma: Combining Control Charts and Fishbone Diagrams  

Six Sigma’s power comes not just in the individual tools but also in their interaction. In the quest for process excellence, control charts and fishbone diagrams complement one other.  

A manufacturing business sees an unexpected spike in faulty goods. Using a Control Chart, the organisation may determine if the defect rate has risen over acceptable levels, suggesting a possible problem. However, the Control Chart alone may not reveal why the defect rate has grown. This is where a Fishbone Diagram can help. The organisation may use the figure to methodically analyse the likely causes of the increasing defect rate, taking into account elements such as man, machine, technique, material, and measurement. This tool combination enables  


Six Sigma is a strategy that gives substantial tools for businesses to achieve the highest levels of quality and efficiency. Control charts and Fishbone Diagrams are critical components of the Six Sigma toolkit. While Control Charts provide process stability and predictability, Fishbone Diagrams help decipher the complex web of factors contributing to problems. Their partnership allows firms not only discover issues rapidly but also to pinpoint the root causes of those problems for targeted change. Six Sigma and its tools will remain vital companions for continuous improvement and excellence as businesses encounter new difficulties and opportunities.