# Chi square and normal distribution relationship

### Chi-squared distribution - Wikipedia

Define the Chi Square distribution in terms of squared normal deviates tables) and the relationship between categorical variables (contingency tables). Notation: • N(μ, σ) will stand for the normal distribution with mean μ and standard deviation σ. Definition: The chi-squared distribution with k degrees of freedom is the distribution of a .. Using this relationship, it is possible to show. Y. Y. Y. Y. Please check out the answer of mine under a similar question thread. answer to What is an intuitive explanation for how the t-distribution, normal distribution.

The calculator is free. It can found in the Stat Trek main menu under the Stat Tools tab.

Or you can tap the button below. On average, the battery lasts 60 minutes on a single charge. The standard deviation is 4 minutes. Suppose the manufacturing department runs a quality control test. They randomly select 7 batteries. The standard deviation of the selected batteries is 6 minutes.

### The Standard Normal and The Chi-Square | STAT /

What would be the chi-square statistic represented by this test? Solution The standard deviation of the population is 4 minutes. The standard deviation of the sample is 6 minutes.

The number of sample observations is 7. To compute the chi-square statistic, we plug these data in the chi-square equation, as shown below.

## Chi-Square Distribution

Problem 2 Let's revisit the problem presented above. The manufacturing department ran a quality control test, using 7 randomly selected batteries. In their test, the standard deviation was 6 minutes, which equated to a chi-square statistic of Suppose they repeated the test with a new random sample of 7 batteries.

What is the probability that the standard deviation in the new test would be greater than 6 minutes? Solution The sample size n is equal to 7.

Relationship between normal and chi-square distribution - 2 of 2

The chi-square statistic is equal to Given the degrees of freedom, we can determine the cumulative probability that the chi-square statistic will fall between 0 and any positive value.

To find the cumulative probability that a chi-square statistic falls between 0 and The calculator displays the cumulative probability: The next result gives the general moments of the chi-square distribution. On the other hand, any gamma distributed variable can be re-scaled into a variable with a chi-square distribution.

## The Standard Normal and The Chi-Square

The chi-square distribution with 2 degrees of freedom is the exponential distribution with scale parameter 2. The chi-square distribution with 2 degrees of freedom is the gamma distribution with shape parameter 1 and scale parameter 2, which we already know is the exponential distribution with scale parameter 2. Recall that if we add independent gamma variables with a common scale parameter, the resulting random variable also has a gamma distribution, with the common scale parameter and with shape parameter that is the sum of the shape parameters of the terms.

Specializing to the chi-square distribution, we have the following important result: The last two results lead to the following theorem, which is fundamentally important in statistics.

This theorem is the reason that the chi-square distribution deserves a name of its own, and the reason that the degrees of freedom parameter is usually a positive integer. Sums of squares of independent normal variables occur frequently in statistics. Here is the precise statement: Note the shape of the probability density function in light of the previous theorem.