Seven Basic Quality tools

Seven Basic Quality tools are Cause and effect diagrams, Flowchart, Checksheets, Pareto diagrams, Histograms, Control Charts and Scatter diagrams. Seven Basic Quality tool is popularly known as 7QC tools in the industry. This uses the famous Edward Deming cycle Plan-Do-Check-Act also known as (PDCA) model to solve the quality related issues. Let us consider one by one.

Cause and effect diagrams: This tool is used to find the cause for a particular defect/effect. The defect or the problem statement is defined and causes for this defect is identified. Then one can use the concept “5 Why’s” to find out the root causes which can be converted to actionable items. When you represent the problem statement and the causes in the form of visual representation, it looks like a fish skeletal hence the name fish bone diagram and is also called as Ishikawa diagram.

Flowcharts: Flow charts depict the flow of the work or the process which is sequence of steps to be carried out. Flowcharts show the activities, decision points, branching loops, parallel paths, inputs, outputs… It uses a model called SIPOC, Supplier-Input-Process-Output-Customer, or the COPIS, Customer-Output-Process-Input-Supplier, model. For example, in the car manufacturing industry, the supplier provides the raw materials as the input, the process manufactures the car which is the output and is used by the customer. The customer provides the feedback which helps in improving the process and in turn the raw materials quality from the suppliers. The workflow logic and the frequency helps in expected monetary value for conformance and nonconformance work to deliver the desired output which in turn helps in estimating the cost of quality.

Checksheets: This is also called as tallysheet used to gather data. Checksheets ensures that all the data has been gathered which helps in identifying potential problems. This helps in inspection to identify the defects. For example there is a product which about 10 cm length which is the expected value. The other possible values which we can get are >10cm or <10cm. Measure all the output and see how many are meeting the expected value and how many or not.

Pareto diagrams: This is also called as 80/20 rule used to find most potential issues or to distinguish between critical vs non-critical. 80/20 rule means 80% of the problems are due to 20% of the causes.

Histograms: It is a bar chart and used to find the central tendency, dispersion and shape of statistical distribution. Also histogram can be used to represent data in no particular order and is not related to time. The bar which is higher can be the reason for the defect or effect.

Control charts: This tool is used to see if the process is stable or not and also to find the measurements are coming within the expected limits. Control charts uses four parameters apart from mean, upper specification limit (USL), lower specification limit (LSL), upper control limit (UCL) and lower control limits (LCL). The mid line will be mean, the line immediately above mean is UCL and the still above that is USL and the line immediately below mean is LCL and the one which still below is LSL. If the measurements are within the UCL and LCL then there is no problem. If the measurements are above the UCL and or below the LCL then it calls for corrective action. There is one more principle called rule of seven. Rule of seven says if the 7 consecutive points are above the mean level or seven consecutive points are below mean level and even though they are within the control limits still it calls for corrective action. USL and LSL can be customer committed values above which the measurements are not acceptable. UCL and LCL are defined within the project level in agreement with stakeholders. UCL and LCL helps in tightening the situation so that we are not touching or deviating the specification limits.

Scatter diagrams: This is also called as correlation charts used to find is there any relation between two variables. The correlation can be positive or negative or zero. Based on positive and or negative it helps in taking further action.

The above 7QC tools can be used as combination.

Seven Basic Quality Tools is used under the process Plan Quality Management, Control Quality. This is also used along with seven quality management and control tools, which is used under the Perform Quality Assurance process.