Section 2.3 Histograms

Normal distribution

A frequency distribution where the frequencies increase to a maximum and then decrease, creating a graph that has symmetry with the left half of the histogram being roughly a mirror image of the right half. The histogram is bell-shaped.

Uniform distribution

A frequency distribution where the values (or classes) appear with roughly the same frequency, so that the histogram bars are approximately uniform in height.

Histogram

A graph of a frequency distribution that has the following characteristics: (1) It consists of bars of equal width drawn touching each other (unless there are gaps in the data). (2) The horizontal scale represents the classes of quantitative data values from our frequency distribution. (3) The vertical scale represents the frequencies and the heights of these bars correspond to the frequency values.

Skewed histograms

A histogram is skewed if it is not symmetric and extends to one side more than the other. (a) Data skewed to the right (positively skewed) has a longer right tail. (b) Data skewed to the left (negatively skewed) has a longer left tail.

Relative frequency histogram

A histogram where the vertical scale uses relative frequencies (as percentages) instead of actual frequencies.