Essential Quality Terms Used in 7QC Tools

The 7QC tools are statistical tools that help individuals, organizations, and businesses resolve quality issues for products and processes. To utilize the 7QC tools it is important to understand the following essential quality terms:

You can read our other blog 7QC: An Introduction to the Seven Basic Tools of Quality here.

80/20 Rule: The 80/20 Rule, also called the “Pareto Principle,” states that 80% of the problems arise from 20% of the sources.

Average: The average, or mean, of a set of sample data is calculated as the sum of the data points divided by the total number of data points.

Central Issue: The problem that needs to be solved.

Control Limits: Control limits are defined as the values that represent the maximum and minimum amount of variation that the averages of data points within subgroups of a process can exhibit. When the subgroups exist beyond the control limits or exhibit specific patterns or trends, then the process is said to be “out-of-control.”

Correlation: Correlation is defined as the level of dependency or association between two variables. Most commonly, linear relationships are evaluated using the Pearson’s correlation coefficient, which is a calculated statistical value.

Cumulative Percentage: The cumulative percentage is the running total of each factor summing to 100%.

Dependent Variable: A dependent variable is the variable, or factor, that changes when other variables change. Outputs from a process, or product characteristics, are typically dependent variables.

Five W’s: The phrase “Five W’s” is short form for asking the Who, What, When, Where, and Why questions.

Frequency Distribution: Frequency distribution shows the variation in a given set of data when the data are tallied into groups.

Independent Variable: An independent variable is the variable, or factor, that does not change when other variables change. Inputs to a process, or process characteristics, are typically independent variables.

Intervals: Intervals are the sub-groups into which data are classified in order to construct a histogram. Intervals are always mutually exclusive, meaning the data points that equal the upper limit of an interval can only exist in that interval and not in the next interval.

Major Categories: The major groupings under which possible causes may be sorted to solve the central issue.

Mode: Mode is the value or number that appears the most often in a set of numbers or data.

Normal distribution: Statistically, a normal distribution is represented in a histogram when a smooth, symmetric curve can be generated from the bars where the mean, or average, is the center of the curve and the rest of it tails off to near zero on either side. Normal distributions are a bell-shaped curve.

Paired Data: When two variables are collected jointly such that for each value of the independent variable (x), a corresponding value for the dependent variable (y) is generated, then the data point (x,y) is said to be paired data.

Population: A population is the entire data set under consideration while analyzing data.

Primary Axis: The primary axis is the Y axis on the left side of the graph used to depict the frequencies.

Primary Causes: The principle causes specific to a particular category.

Range: Range is calculated as the difference between the maximum and minimum observed values of a set of sample data.

Sample: A sample is a smaller subgroup of data that is taken from within the population.

Secondary Axis: The secondary axis is the Y axis on the right side of the graph used to depict the cumulative percentages.

Secondary Causes: The causes derived from the primary causes after further brainstorming.

Standard Deviation: Standard deviation is defined as the amount of variation that exists within a sample data set. The Greek letter “sigma,” σ, is used to represent standard deviation.

Stratified Data: When collected data show tendencies of being divided into more than one subgroup, then the data are said to be stratified.

Stratified Sampling: Stratified sampling is the method of collecting and sorting data from a population into smaller logical segments after sampling takes place.

Subgroup: Subgroup is defined as a small collection of data points, typically between 2 and 10 data points, that are compiled together within a short interval of time. The average of the data points within a subgroup is represented as a single dot in the control chart.

Tally Marks: Tally marks are used to determine quantity. Each tally mark represents the value 1, where I = 1. When the amount of tally marks reaches 5, the fifth tally mark strikes across the previous 4 marks to be recorded as a fifth tally, ||||. The tally marks continue as single tallies until the next multiple of 5, the value 10, is to be recorded, |||| ||||. [Put slashes across the 4 tallies here and at the 5 location.]

Tertiary Causes: The causes derived from the secondary causes after further brainstorming.

Variable: A variable is a type of characteristic that can be used to separate/segregate data into groupings that affect a given process or outcome, and it can change according to outside influences like time, place, and standards.

To learn more about these Seven Basic Tools of Quality Control, and to learn how to apply these tools to solving quality problems by viewing examples, check out the online 7QC courses in the THORS Academy Library, brought to you by THORS eLearning Solutions.


7QCs: An Introduction to the Seven Basic Tools of Quality Control

Quality control. Of course it is important. When producing parts or products, the ability to monitor, troubleshoot, and adjust manufacturing processes is necessary for companies to remain efficient and competitive. If products are to be made consistently to a required standard, the methods of manufacturing must be measurable, adjustable, and repeatable.

In order to achieve these standards, logical, data driven approaches to finding acceptable solutions can be used, such as the 7QC tools, or the Seven Basic Tools of Quality Control. The 7QC tools are statistical tools that help individuals, organizations, and businesses resolve quality issues for products and processes. They are called basic tools because they are suitable for people with little formal training in statistics and because they can be used to solve the vast majority of quality-related issues.

7QC tools include:

Check Sheets

Check sheets are used to collect data in order to understand the qualitative and quantitative variables that can affect a process. When recording data on a check sheet, check marks or tally marks are used to indicate the amount of what is being collected, which helps in understanding the progress, defect patterns, and even causes for defects.

Check Sheets

Control Charts

Control charts are graphs used to represent process performance over time. Subgroups of data points are collected and compiled together within a short interval of time. The average of the data points within a subgroup is represented as a single dot in the control chart. The amount of variation that exists within a sample data set is the standard deviation, which is used to determine the control limits. When the subgroups exist beyond the control limits or exhibit specific patterns or trends, then the process is said to be “out-of-control.”

Control Charts

Fishbone Diagrams

Fishbone diagrams, also referred to as cause and effect diagrams, are a quality control brainstorming tool used to help identify the root cause or causes of an issue by looking at all possible variables.

When using these diagrams, a central issue or focal point, such as a defect or quality problem, is placed at the head of the “fish.” The “bones of the fish” serve as a way to visually organize all possible variables, or causes, that may have caused the central issue, and sort ideas into categories to investigate further.

Fishbone Diagrams


Histograms are a type of bar graph used to represent the frequency distribution, or how often each different value in a set of data occurs. It is created by grouping the data you collect into “cells” or “bins.” The histogram is the most commonly used graph to assess process behavior and demonstrate if the data follow a normal distribution, or bell-shaped curve.


Pareto Charts

Pareto charts are a combination of bar and line graphs that provide a visual representation of how often the various issues affecting a process are occurring. Pareto chart derives its name from the use of the Pareto Principle, which states “80% of the effect comes from 20% of the causes.” Using this chart, professionals can decide where to place priority and focus.

Pareto Charts

Scatter Diagrams

Scatter diagrams, also called scatter plots, are graphs used to visually represent the relationship between two variables in order to quickly identify the correlation between them.

This tool is used to determine the type of relationship that exists between the inputs to the process, or process characteristics, and the outputs from a process, or product characteristics.

Scatter Diagrams


Stratification is a method of dividing data into subcategories and classifying data based on group, division, class, or levels that helps in deriving meaningful information to understand an existing problem.


To learn more about these Seven Basic Tools of Quality Control, and to learn how to apply these tools to solving quality problems by viewing examples, check out the online 7QC courses in the THORS Academy Library, brought to you by THORS eLearning Solutions.

COVID Featured

Five Plans to Prepare Employees for Returning to Work Post COVID-19

Easing back to a normal work schedule after COVID-19 will take time and strategy. Many different measures must be in place in order to prepare the workforce for new protocols centered around mitigating the after-effects of COVID-19. A response team may be appointed in order to make necessary decisions and changes to company policies, which may include members from legal, human resources, and IT and communications, to name a few.

To ensure and protect the safety of all workers, it is suggested to implement the following five main types of preparation plans.

Step 1 A Contingency Plan for Infectious Disease & Response

A contingency plan for infectious disease and response is a proactive process used to identify and analyze the potential risks that the possible future events may pose and to formulate preventive measures for maintaining the regular operations of an organization.

It is not yet known if the pandemic COVID-19 will be an endemic disease to regularly combat in the future. Regardless, suggested best practices are to implement measures based on past experiences with other communicable diseases, such as SARS and MERS.

When developing a contingency plan, first, the identified potential risks are listed, and then appropriate preventive actions to mitigate them are determined and implemented based on the impact of the potential risk.

By ensuring safety of personnel and infrastructure, an organization will be able to avoid adversities and function efficiently without any interruptions.

Contingency plans for each manufacturing or service industry will be unique depending on their geographical location, size, weather conditions, and accessibility. In the development of a company’s specific contingency plans, regularly consult organization’s websites for additional resources, such as the Centers for Disease Control (CDC), the World Health Organization (WHO), and the Occupational Safety and Health Administration (OSHA).

2) Infection Control Measures

Creating a plan for infection control begins with working with local and state health departments in order to follow current and appropriate guidelines and protocols. Establish hygiene measures which assist in illness prevention. Remind employees also about the use of, and where to obtain, necessary supplies such as hand sanitizer, tissues, and cleaning products.

Some of these directives could include the following:

  • Reminding about cough and sneeze etiquette
  • Hand washing and hand sanitizing
  • Increasing distance between people to at least 6 feet
  • Staggering shifts or schedules
  • Creating a remote working or delivery program
  • Encouraging appropriate additional PPE
  • Increasing cleaning measures

When a plan is determined, the reliable and up-to-date guidelines for employees to follow should be communicated and posted in highly visible areas.

3) Additional Policies

Policies and procedures for illness reporting during COVID-19 must be in place. Every company should evaluate their current procedures to incorporate specific rules pertaining to the coronavirus situation. These could involve procedures such as a flowchart on how each level of illness is handled, or policies in place for employees to know that their job is still secure if they need to call off due to illness. The Americans with Disabilities Act, or ADA, provides additional guidelines about the amount of information that should be provided to the employer, as well as the rights of the employee’s health privacy as it could be related to a disability.

According to Mayer Brown in the March 09, 2020 article, Coronavirus: 10 Steps US Employers Should Take to Maintain a Safe Workplace in the Face of a Public Health Emergency, employers should also “be mindful of the interplay between sick leave laws and policies, the FMLA, ADA, HIPAA and Workers’ Compensation.”

Some of the suggested actions include policies and guidelines for:

  • Teleworking and video conferencing
  • Length of time for staying at home until symptom free
  • Flexible, non-punitive leave to care for sick family members

More information can be found in the Ohio Department of Health’s Amended Director’s Stay at Home Order, or review similar information from your state or province.

4) Training for New Policies

A program and schedule for training employees on new guidelines should be in place. Many new rules could be overwhelming and confusing, and it may be required to determine whether all employees received the correct information.

Training should be instituted on topics such as:

  • COVID-19 exposure, who is at risk and how – what interactions or tasks increase exposure
  • Safe distancing practices both at the workplace, and outside the workplace
  • What to do in case of illness, and questions and answers regarding individual concerns
  • New policies for PPE, cleaning surfaces, and other topics

Training should be implemented in a manner that maintains safe distancing, such as with:

  • Live or Recorded Video conferencing, using tools such as Zoom or Microsoft Teams
  • On-Line Training Courses, such as THORS eLearning Solutions COVID-19 Video and Assessment

For best assurance of the receipt of the training, it is recommended that the training include some or all of the following opportunities:

  • Access to someone to ask questions and receive answers
  • Self-assessment prior to and after the training, to determine comprehension
  • Access to the training remotely, at any time of the day, and as many times as necessary for understanding
5) Assess & Track Employee's Compliance

It may be necessary to assess and track the employee’s compliance within the company. This can involve creating a compliancy assessment and implementing record keeping and tracking to ascertain whether employees have understood the new measures to follow.

An assessment tool, such as MAGNI, would be useful in order to remove the uncertainty from compliancy analysis. With MAGNI, an organization can customize their own compliancy solution by creating their own assessment with questions that reflect the standards the employees must follow.

Here’s how MAGNI works:

1- Each company determines the subject matter they wish to inform or train their own workforce on.

2- The company then follows the instructions in MAGNI’s assessment tool to create the questions for their assessment. These questions should reflect the points that are most important for the employees to know, and for the company to know if the employees understood.

3- The administrative access allows the company to see who has taken the assessment and what their score was. The tracking of score improvement during re-takes, as well as timely re-assessments to meet compliancy rules can be scheduled.

With this list of the five main plans to prepare employees for returning to work after the COVID-19 order, as well as tools and resources available, THORS eLearning Solutions and MAGNI hope to empower organizations to minimize the impact of the changes due to COVID-19 on businesses and communities, and increase the awareness and safety of everyone.

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