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# Variability

### Descriptive statistics terms related to measuring variability in data

Question | Answer |
---|---|

variability | The degree to which the scores in a data set differ from each other. (syn: dispersion, spread) |

dispersion | The spread of scores in a data set so that they differ from each other. (syn: variability, spread) |

range | Distance from the highest score to the lowest score; a measure of variability. |

inclusive range vs exclusive range | The exclusive range is the high score minus the low score (i.e., h-l). The inclusive range adds 1 to the exclusive range, so that the low score is still part of the range (ie., (h-l)+1 for the formula). |

interquartile range (IQR) | The distance from the score at the 75th percentile (Q3) to the score at the 25th percentile (Q1) , computed as Q3-Q1. The range of the middle half of the cases. |

standard deviation | Indicates the standard or "average" distance of a score from the mean of the scores. Computed differently for data representing a sample and a population. Square root of the variance. In the original units of measurement. |

variance | A measure of the variability in a set of data whose unit is squared deviations of the original unit. Square of the standard deviation. Computed differently for data from a sample and a population. |

deviation | Deviation usually refers to the distance from a score to the mean of a data set, although a deviation can be computed around the median or any other designated number. |

STDEV | Excel function to compute the standard deviation of data representing a sample. Uses n-1 in the denominator. |

STDEVP | Excel function to compute the standard deviation of data for an entire population, using n in the denominator. |

mean deviation | Sum of the absolute value of the deviations. Not often used because of computational difficulties. |

biased vs unbiased estimate | Sample data are used to represent a larger population. If a statistical procedure puts a systematic bias into the estimate, it is less desirable than a statistic that is unbiased. |

VAR | Excel function for computing the variance of data from a sample. |

VARP | Excel function for computing the variance of data for a population. |

spread | The degree to which data vary from each other, how spread out they are across the range. (syn: variability, dispersion) |

Created by:
ebogue