## Histograms

A histogram is a type bar chart using intervals on the x -axis, with the modification that the interval sizes are not fixed. The frequencies are defined by the areas of the bars, and the y – axis is not a frequency axis, but a frequency density axis. A histogram is better able to represent data because it can be used where the data is irregularly grouped. The heights of a group of fictitious children are summarised in the table below.

Height | Frequency |

65 – 75 | 2 |

75 – 80 | 7 |

80 – 90 | 21 |

90 – 105 | 15 |

105 – 110 | 12 |

We construct a Frequency Density Column, usingobtaining the table

Height | Frequency | Frequency Density |

65 – 75 | 2 | 2/10 = 0.2 |

75 – 80 | 7 | 7/5 = 1.4 |

80 – 90 | 21 | 21/10 = 2.1 |

90 – 105 | 15 | 15/15 = 1.0 |

105 – 110 | 12 | 12/5 = 2.4 |

We can now draw the histogram.