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How to Calculate the Critical Value of a Bell Curve

Statistics is the art and science of making larger assumptions based on limited data. The bell curve is a visual representation of where the data lies. To the right of the center line, values are positive, to the left they are negative. In a normal distribution scenario, it is assumed that the positive and negative values are mirror images. Therefore, to determine the critical value of the bell curve, you need to decide upon a few criteria.

Degree of confidence that you desire
Z table

Instructions

- 1
  Divide your confidence level by 2. If your confidence level is 95%, your answer will be .4750.
- 2
  Look in the Z table for .4750. If your exact number is not present, then take the one closest to it.
- 3
  Find the corresponding number in the row at the far left column, which is 1.9.
- 4
  Find the corresponding number in the column at the top, which is 0.06.
- 5
  Add the two together and you have 1.96. This is an absolute value and is correctly identified as +/- 1.96%.
- 6
  Multiply 1.96 by 2. The result is 3.92.
- 7
  Subtract .0392 from 1 and you have 96.8%, which is the area of the bell curve covered by the critical value.

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