How to Find Critical Value: A Comprehensive Guide


Hello DAPPS Lovers! If you’re interested in statistics, then you’ve probably heard of the term “critical value” before. Critical value is an important concept in statistics that helps determine the significance of a hypothesis test. In simple terms, it is the value that divides the critical region from the non-critical region under a given distribution. Understanding how to find critical value is essential in statistical analysis.

In this article, we’ll take a deep dive into everything you need to know about how to find critical value. We’ll explore its strengths and weaknesses, provide a step-by-step guide to calculating critical values, and answer some common questions about this important statistical concept.

The Importance of Critical Value in Statistics

Before we dive into how to find critical value, let’s first understand why it’s so important. In statistics, we often use hypothesis testing to determine whether a sample is significantly different from a population or if any observed differences occurred by chance. Hypothesis testing involves specifying a null hypothesis and an alternative hypothesis, defining a significance level (often denoted by 𝛼), and then using a test statistic to determine whether to reject or fail to reject the null hypothesis.

The test statistic is compared to the critical value to determine statistical significance. If the test statistic falls within the critical region (i.e., the region where we reject the null hypothesis), we reject the null hypothesis. If the test statistic falls within the non-critical region (i.e., the region where we fail to reject the null hypothesis), we fail to reject the null hypothesis.

Therefore, finding the critical value is crucial in hypothesis testing. It helps us determine the significance of our test statistic and make informed decisions based on the results.

Strengths of Finding Critical Value

One of the strengths of understanding how to find critical value is that it provides a rigorous framework for hypothesis testing. Hypothesis testing can be a complex and subjective process, and having a clear and structured approach helps ensure that decisions are made based on evidence rather than intuition.

Another advantage of finding critical value is that it allows for greater flexibility in hypothesis testing. By adjusting the significance level (𝛼), we can prioritize either Type I or Type II error. This flexibility allows us to make informed decisions based on contextual factors that may influence the costs and benefits of different types of errors. For example, in medical testing, the consequences of a false negative may be more severe than the consequences of a false positive. Adjusting the significance level can help ensure that we make decisions that prioritize minimizing the most significant errors.

Weaknesses of Finding Critical Value

Despite the strengths of finding critical value, there are also some weaknesses to consider. One potential drawback is that critical value requires knowledge of the underlying probability distribution. In some cases, this knowledge may not be available or may be difficult to obtain, which can limit the usefulness of this approach.

Another potential weakness of critical value is that it can be overly conservative. By focusing on minimizing Type I error, we run the risk of increasing Type II error (i.e., failing to detect a significant effect when one exists). This bias towards avoiding false positives can lead to missed opportunities for discovery, particularly in areas where exploratory research is needed.

How to Find Critical Value: Step-by-Step Guide

Now that we understand the importance of finding critical value in statistics let’s learn how to calculate it. There are a few steps involved, which we’ll outline below in detail.

Step 1: Identify Your Probability Distribution

The first step in finding critical value is identifying the probability distribution for your variable of interest. The most commonly used distributions in statistics are the normal distribution, t-distribution, and chi-square distribution. Knowing which distribution to use depends on the nature of your data and the type of hypothesis test you want to run.

Step 2: Identify Your Significance Level

Once you’ve identified your probability distribution, you need to define your significance level (often denoted by 𝛼). This is the probability of rejecting the null hypothesis when it is true. Commonly used significance levels include 0.05, 0.01, and 0.001. The choice of 𝛼 depends on the context of your research and the costs and benefits associated with different types of errors.

Step 3: Determine Your Degrees of Freedom

The next step is determining your degrees of freedom (df). This will vary depending on the specific distribution you’re using and is often influenced by the sample size. For example, if you’re using a t-distribution to analyze a sample with 10 observations, the degrees of freedom would be 9.

Step 4: Look Up the Critical Value

Finally, you can use a critical value table or calculator to identify the critical value for your specific distribution, significance level, and degrees of freedom. The critical value is typically denoted by the symbol 𝑡, 𝑧, or 𝜒², depending on the distribution used. For example, if you’re using a t-distribution, you’ll be looking up 𝑡 values.

Example Calculation

Let’s say that you have a sample of 25 observations and you want to run a two-tailed hypothesis test on the mean. Your significance level is 0.05. To find the critical value for a t-distribution with 24 degrees of freedom, you would use a 𝑡 table or calculator and find the value associated with a probability of 0.025 (half of your significance level). In this case, the critical value would be approximately ±2.064.

Table of Critical Values

Probability t-Distribution Z-Distribution Chi-Square Distribution
0.95 1.711 1.96 3.841
0.99 2.626 2.58 6.635
0.999 3.707 3.29 10.828
0.9999 4.317 3.89 15.136

FAQs About Finding Critical Value

Q1. What does critical value mean?

A: Critical value is the value that separates the critical region from the non-critical region under a given probability distribution.

Q2. What is the significance level?

A: The significance level (often denoted by 𝛼) is the probability of rejecting the null hypothesis when it is true.

Q3. How do you determine degrees of freedom?

A: Degrees of freedom depends on the probability distribution being used and is calculated as the sample size minus one.

Q4. What is the difference between Type I and Type II error?

A: Type I error is rejecting the null hypothesis when it is actually true. Type II error is failing to reject the null hypothesis when it is actually false.

Q5. Can critical value be negative?

A: Yes, critical value can be negative for distributions such as the t-distribution.

Q6. What happens if the test statistic is greater than the critical value?

A: If the test statistic is greater than the critical value, we reject the null hypothesis and conclude that the observed effect is statistically significant.

Q7. How can I calculate critical value for a chi-square distribution?

A: Critical value for the chi-square distribution can be calculated using a chi-square critical value table or an online calculator.


In conclusion, understanding how to find critical value is crucial in hypothesis testing and statistical analysis. By following the steps outlined in this article, you can calculate critical values for various probability distributions and significance levels. While critical value has its strengths and weaknesses, it is an essential tool for making informed decisions based on statistical evidence.

Take the time to master this important statistical concept and use it to your advantage in your research and professional endeavors. Remember to always prioritize evidence-based decision-making and use critical value to support your conclusions.


The information provided in this article is for educational purposes only and should not be construed as legal, financial, or professional advice. The author and publisher of this article make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties. The advice and strategies contained herein may not be suitable for every situation. You should consult with a professional where appropriate. Neither the author nor publisher shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

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