How to Calculate P Values in Chi Square

A butterfly flaps its wings in China and a flood occurs in North America. Coincidence? Probably. In statistics, a "P-value" is a probability between 0 and 1 designed to give you an indication of the chance that your samples mean deviations from each other is a "result of a coincidence of random sampling." In other words, "if the P value is 0.03, that means that there is a 3 percent chance of observing a difference as large as you observed even if the two population means are identical." You can use several means to calculating a p-value, but it is naturally a result of a chi-square test performed on a scientific calculator.

Things You'll Need

  • Scientific calculator, such as TI-83 Plus or TI-84 Plus
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Instructions

    • 1

      Turn the calculator on. Enter your data table into a matrix as follows: Press the "2nd," "Matrix." Use the arrow keys to move to the "Edit" menu and select the matrix, usually the first, "1:[A]."

    • 2

      Enter the dimensions of your data matrix. For a matrix of 3 x 5, for example, your calculator screen will read:

      Matrix [A] 3 X 5

    • 3

      Enter your observed values by pressing the number and pressing "Enter" after each entry.

    • 4

      Press "Stat" when your data entry is complete. Use the arrow keys to move the cursor to "Tests." Scroll down to the "x2-Test." Press "Enter."

    • 5

      Enter the name of the matrix with the observed frequencies -- [A] in this case --

      and name a second matrix, such as [B], in which the expected frequencies will be stored.

    • 6

      Select "Calculate" with the arrow keys and press "Enter." The calculator will return the chi-square, x2, result; the P-value or the probability value; and the df, or degrees of freedom, number.

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