# How to Calculate Critical Values for Statistical Hypothesis Testing with Python

In most professions, we make the hypothesis, in which a proposed explanation is made by using limited evidence. This evidence is used as the starting point to continue the further investigation. Hypothesis testing calculates the probability that checks the given hypothesis is true or not by using the data sets. Use the p-values to interpret the result of hypothesis tests. In statistical testing determining the critical values is a tough task for many people. So, to make the calculations easy you can try the left and right critical value calculator. In this article, you will discover the critical values, their importance, uses, and their calculation in python.

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**Why we use critical values?**

In most of the hypothesis tests, p-values are used to interpret the result of the distribution. Some of the test alternative methods are used to do the calculations for test statistics directly instead of using the p-values. Finding critical values is not so easy sometimes. So, using an online critical value calculator is the best option to calculate the P value of different distributions. However, critical values are used to define the intervals for expected or unexpected observations in the distributions.

**What are critical values?**

In statistical testing, a critical value is a point on the distribution used to compare with test statistics to determine whether to accept or reject the null hypothesis. You can declare the null hypothesis as statistical significance if the absolute value is greater than the critical value of the distribution. Usually, critical values are difficult to calculate but with the assistance of an online left and right critical value calculator, the calculations become easier. Here, the critical value is considered in the context of probability and population distribution.

## How to use the critical values:

Critical values that are calculated used to interpret the results of the hypothesis test. The observed values of the population beyond the critical values are known as the “critical region” or “region of rejection”. The critical value is a value that appears in the statistical tables such as z critical value table, t critical value table, etc. it indicates that on the base of computed value the null hypothesis is rejected. Maybe the statistical test would be one tailed or two tailed test.

**One-Tailed Test:**

The one-tailed test has a single critical value, which can be on the left or right side of the distribution. Usually, the critical value of a one-tailed test is on the right side of the distribution for instance Chi-square distribution. For convenience, you can try an online critical z value calculator that allows you to find the critical values of the chi-square distribution.

The test statistic for the distribution is compared to the calculated critical value. The null hypothesis is not rejected, when the value of the test statistic is less than or equal to the critical value. If the situation is the opposite, then the hypothesis will be rejected. This interpretation is summarized as follows:

**Two-Tailed Test:**

In a two-tailed test, two critical values of the distribution are used; one value is on each side of the distribution. These values are assumed to be symmetrical for example Gaussian and student’s t distribution.

At the time of using the two-tailed test, the confidence level or Alpha must be divided by 2. The critical value of the distribution will then use the portion of confidence level on both sides of the distribution. The manual calculation for critical values might be difficult, so give a try to an online critical calculator that helps to calculate the critical values of any tail.

**How to Calculate Critical Values in Python:**

To calculate the critical value a specific function is used, in which the given probability or significance will return the observations from the distribution. There are two types of density functions for the distribution the first one is PDF (probability density function) & the second one is CDM (cumulative density function).

By using the ppf() function on the distribution we can calculate the percent point function. You can also calculate the ppf() by using the inverse survival function known as isf() in SciPy. Instead of complex calculations on the paper, you can use the left and right critical values calculator that finds the critical values in both sides of the distribution.

**Conclusion:**

In this article, we discussed the critical values, their importance & uses, and their manual calculation. We also discuss how to calculate critical values in python. Statistical hypotheses are the techniques to determine the critical values. The critical values are used to check the validity of the hypothesis.