68-95-99.7 Rule

Definition

The 68-95-99.7 Rule describes how data is distributed in a normal distribution. It states that approximately 68% of the data falls within one standard deviation, 95% within two standard deviations, and 99.7% within three standard deviations from the mean.

5 Must Know Facts For Your Next Test

1. Approximately 68% of the data in a normal distribution lies within one standard deviation from the mean.
2. Around 95% of the data in a normal distribution is found within two standard deviations from the mean.
3. About 99.7% of the data in a normal distribution falls within three standard deviations from the mean.
4. The rule helps to quickly estimate probabilities and understand the spread of data in a normal distribution.
5. It is also known as the Empirical Rule or the Three-Sigma Rule.

Review Questions

• What percentage of data lies within two standard deviations in a normal distribution?
• How does the Empirical Rule relate to standard deviations?
• What are other names for the 68-95-99.7 Rule?

Related terms

Standard Deviation:

A measure of how spread out numbers are around the mean of a dataset.

Normal Distribution:

A probability distribution that is symmetric about its mean, showing that data near the mean are more frequent in occurrence than data far from it.

Mean:

The average value of a set of numbers, calculated by dividing their sum by their quantity.