# Statistic

- Anything that can be calculated from a sample of data. The most common use of the word is for summary measures such as the sample mean and sample standard deviation, although graphical displays such as histograms are also statistics. When referring to the population mean or standard deviation, the term parameter is used.

**Descriptive Statistics**- Involves numerical or graphical summaries of data.

**Inferential Statistics**- Statements are made about population parameters based on sample statistics.

Average Deviation | The absolute value of the difference from the mean for each data value, summed, then divided by the number of values. |

Mean | The average, between the extremes. The sum of all values in the data, divided by the number of values. |

Median | A statistic which measures the centre of a set of data by finding that value which divides the data in half. |

Skew | An expression of the so-called "third moment". A tendency for a distribution to lean to the right (or left, when negative), showing a fast dip from the central mean but having an extended tail. |

Standard Deviation | Standard deviation is the square root of the variance, i.e. the square root of the mean of the squares of the deviations from the mean value of a vibrating quantity. |

Standard Error | The standard error of the mean. The standard deviation divided by the square root of the number of data values. |

Variance | The square of the difference from the mean for each data value, summed and divided by one less than the number of values. |

**See also: **Average Deviation, Mean, Median, Probability, Skew, Standard Deviation, Standard Error, Standard Normal Distribution, Summary Statistics, Variance.

**Subjects: ** Statistics

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