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What are Critical Values?

An Overview of Critical Values: Definition, Calculations, and Examples

In statistics, the critical value is vital for correctly reflecting a variety of features. In

addition to validity and accuracy, the critical value can be useful for disproving

hypotheses when they are tested. Understanding critical value and how to calculate it is

vital for evaluating other statistical functions, such as margin of error and significance,

whether you're taking a statistics course or just curious about how these concepts


In this post, we'll go over what critical value is, how to calculate it, and an example of

calculating t critical value to illustrate the method.

Critical Value - Definition

The critical value in statistics is the measurement statisticians use to quantify the margin

of error within a collection of data, and it is represented as:

Critical Value = 1 - (Alpha / 2)


Alpha = 1 - (confidence level / 100).

The critical value can be expressed in two ways: as a Z-score connected to cumulative

probability and as a critical t statistic equal to the critical probability. Furthermore, the

critical value explains numerous aspects of the margin of error that statisticians may use

to assess the quality of the data under consideration.

Assume a statistician is examining population research on the impact of sunshine on

mental disorders. There will be a margin of error within a population sample size that

specifies the rate at which any differences, such as outliers, will arise within the data


Significance of Critical Value

The critical value is vital in determining validity, accuracy, and the range within which

mistakes or inconsistencies within the sample set can occur. This figure is critical in

estimating the margin of error. Similarly, the critical value might provide information on

the properties of the sample size under consideration.

For example, representing the critical value as a t statistic is vital for precisely assessing

small sample sizes or data sets with unknown standard deviations. Expressed as the

cumulative probability, or Z-score, the critical value provides for a more precise

examination of a larger data set, often with 40 or more samples. The critical value

becomes incredibly significant for examining validity and accuracy, as well as disparities

among different population sizes that you research.

How to calculate Critical Value?

Calculating the critical value of a data set is a simple process. Depending on your

sample size, you may also represent the critical value in one of two ways. The following

steps will show you how to achieve it:

1. Find Alpha Value

Before computing the critical probability, calculate the alpha value using the formula:

Alpha value = 1 - (the confidence level / 100).

The confidence level shows the likelihood that a statistical parameter is also true for the

population being measured. This number is usually expressed as a percentage. A

confidence level of 95 percent within a sample group, for example, suggests that the

specified criteria have a 95 percent chance of being true for the entire population. Using

a confidence level of 95%, you would complete the following calculation to determine

the alpha value:

Alpha = 1 - (95/100) = 1 - (0.95)

Which equals 0.05. The alpha value in this example is 0.05.

2. Find the Critical Probability

Calculate the critical probability using the alpha value from the first formula. This is the

critical value, which may then be expressed as a t value or a Z-score. You can also use

t value calculator to find t critical value.

Completing the formula to obtain the critical probability using the preceding example's

alpha value of 0.05:

1 - (0.05 / 2) = 1 - (0.025) = 0.975 is the critical probability (p*). In this case, the critical

probability is 0.975, or 97.5 percent.

3. For small sample sets, use t critical value

The critical t statistic is the right formulation for the critical probability when measuring a

small sample size. As the t statistic, express the critical probability of 97.5% as


The sample size minus one equals the degree of freedom (df). This implies that dividing

the number of samples in your study by one will give you the degree of freedom. So, if

your sample size is 25, deduct one from this figure to get the degree of freedom. In this

situation, the answer is 24.

4. For big data sets, use z critical value

For population sizes more than 40 samples in a set, the critical value can be expressed

as a Z-score. The cumulative probability of the Z-score should be equal to the critical

probability. The cumulative probability is the likelihood that a random variable will be

less than or equal to a certain value. This probability must be equal to or greater than

the critical probability or value.

z critical value calculator can assist you to calculate z critical value using significance

level only.

How many types of critical values are there?

You may use several critical value testing methodologies to assess the statistical

significance of a particular population or sample. The statistical significance will inform

you whether or not the findings of your tests are valid. The following are the critical

value systems that statisticians used when calculating significance:

1. Z Critical Value

Z critical values are the standard scores that may be calculated from a data collection.

The Z-score indicates how far a specific data point deviates from the sample mean. This

sort of critical value will inform you how many standard deviations your population mean

is above or below the raw score.

2. T Critical Value

T critical values are the results of standardized testing. The SATs, for example, is an

example of a standardized test that can result in t-scores. In statistics, the t-score allows

you to turn an individual test score into a standardized form that you can subsequently

compare to other test results.

T critical values can also be calculated using a table. If you are not comfortable using

tables, you can use t table calculator to find the critical value of t.

3. Chi-square Value

Chi-squares are derived from two types of chi-square tests: goodness of fit chi-square

tests and independence chi-square tests. The goodness of fit chi-square test

determines whether a small collection of sample data is representative of the entire

population. In the independence chi-square test, you will compare two variables to

discover their connection.

4. F Critical Value

F critical value is a value on f distribution. It is used to determine the significance of the

conducted test. It can be calculating by dividing two mean squares. Mostly, it is used in

ANOVA - analysis of variance.

This article is published with permission.

The Six Sigma Methodology

Learning all of the Six Sigma material through any certification course or tutorial can be overwhelming and challenging.

Not familiar with Six Sigma? Click here to learn what many CEO's and others are learning and adopting for their companies.

Thoroughly understanding the array of continuous improvement tools, their value, and meaning takes more time and application than a course allows. This material is presented in a simple format to help comprehend the basic principles in smaller lessons.

This site is also designed to help those use their training and skillsets to find a career. Click here to search for job openings related to Six Sigma.

This website will provide clarity and knowledge of each step of the process through the use of visual aids and roadmaps. Understanding the basics is essential prior to leading a team as a White Belt, Yellow Belts, Green Belt, Black Belt, Master Black Belt, or any other type of continuous improvement leader and project manager.

The tools provide the project team with guidance; they will not directly improve the process. Proper employment of the tools will guide critical decisions and monitor control. Understanding when and which to apply will accelerate project execution.

The methodology is disciplined and structured; it is a system. There are frequent applications of statistical tests but being overly number bound has its limitations, the results of statistical tests should be checked and balanced with reason.

Much of the traditional emphasis of quality improvement and continuous improvement programs is placed on waste reduction and shifting process performance toward a target.

The Six Sigma methodology strives to achieve more...and sustain the achievement. It is a collection of these tools, applied in a systematic manner, with an emphasis on variation reduction for process improvement (DMAIC) and product development (DFSS)

Six Sigma is a business management strategy for which its foundation is typically credited to engineer Bill Smith at Motorola in 1986. The program picked up momentum through substantial gains from another engineer, Jack Welch Jr. while serving as CEO of General Electric.

Six Sigma in an Organization

Six Sigma structure in an organization

A Six Sigma program within a company usually creates its own infrastructure. Six Sigma "Belts" are often thought to be those with engineering backgrounds. While there are many that succeed due to their statistical background it is certainly not the requirement. In fact, each company should train a wide variety of backgrounds as their change agents to lead the company on the Six Sigma journey.

Candidates should come from human resources, finance, clerical, operations, sales, marketing, quality control, engineering, production control, purchasing, supply chain, R&D, maintenance, and any other department within an organization.

The CEO and Board of Directors are at the highest level of a corporation. They have decided to embrace and implement the methodology in their company.

Upper Management representative or Vice-President of Six Sigma They are responsible for all the inputs and outputs (profits related to Six Sigma projects) of the program reporting to the CEO.

Champions or Sponsors are leaders trained to select and prioritize Six Sigma projects that deliver the goals and objectives of the company. Champions will select and mentor Six Sigma project leaders such as Black Belts and Green Belts.

Champions are frequently engaged in the beginning of DMAIC and DFSS projects in the Define phase to ensure the scope is being maintained and going in the right direction.

Master Black Belts

Master Black Belts (MBB) report to the VP of Six Sigma and are the highest level of "belt". Some may specialize in DMAIC, DFSS, or both methodologies but they are subject matter experts in Six Sigma material with advanced statistical knowledge.

Companies that focus a lot of resources on research and development may be more interested in DFSS experts. Those that are process oriented may have a need for more DMAIC experts. MBB's may lead some projects that are very large in scope with a high impact to the organization. They are also responsible for teaching programs, development of materials, and the Six Sigma certification program.

The MBB's are the high level teachers of Six Sigma material as well as Black Belts. The effectiveness and use of the tools is a reflection of an organization's teachers. When the learners haven't learned, the teachers haven't taught. The proper application of the methodology starts with the MBB's. 

Six Sigma Black Belts (SSBB)

Black Belts work for the MBB. They are usually full time Six Sigma employees carrying out the duty of a change agent. Black Belts work projects smaller in scope than the MBB but larger than the Green Belts (GB). Black Belts are also be subject matter experts and will often conduct training, mentoring, and develop new six sigma material.

Often they will lead a team that has Green Belts as team members, but are not required. It is more important to engage critical stakeholders of the project that are willing to accept change and participate. With cross-functional representation the subjective component of the methodology will add more value.

Black Belts have usually been selected as high caliber talent and capable of leading transformation. The technical skills are half of the skillset, being able to change the culture and manage the project is the other.

Six Sigma Green Belts (SSGB)

Green Belts often lead projects themselves, and normally have an assigned Black Belt as a mentor. These teams may have other Green Belts and also include stakeholders such as operators, supervisors, human resources, finance, and anywhere else in the company. Anyone with a stake in the outcome and is willing to participate can be on the team. Green Belts often continue to hold their existing job and responsibilities while leading a project.

Six Sigma Yellow Belts (SSYB)

Yellow Belts typically go through about 15-20 hrs of training and an exam. At this secondary level are the introduction of metrics and basic improvement methodologies. Yellow Belts retain their existing job and participate on Six Sigma teams as needed and will have responsibilities from data collectionwaste identification, to basic statistical analysis. 

Six Sigma White Belts (SSWB)

White Belts are trained in general principles of Six Sigma and Lean Manufacturing. Certification usually requires one day of training and an exam. When this level exists within a company's Six Sigma infrastructure it is considered the first level. White belts become accustomed to the structure and format of a DMAIC or DFSS project.

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