Histograms represent the distribution of frequencies , so this type of diagram is used mainly in the field of statistics. In them it is possible to read how often certain values appear in a class (a group of values). For this, both the width and the height of the bars are used. From the width of the bars it is possible to deduce the size of a class, which is one of the advantages of histograms: when you create a chart of this type, it is possible to determine the size of the class independently.
Example: suppose that we want to represent graphically, with the help of a histogram, the results of some throws in a children's sporting event. Those responsible measure different launch distances that they will later represent graphically. To do this, they divide the measurement values into different classes. These should not be presented uniformly: the width of the bar indicates the size of each class on the histogram..
However, it is recommended to maintain uniformity at least in the middle of the diagram, as this strengthens the understanding of the graph. A class can be composed, for example, of launch lengths between 30 and 34 meters. The individual data is then divided into classes and the frequency of the classes is determined in this way .
To determine the height of the bars it is also necessary to calculate the so-called density. To do this, the number of values belonging to a class is divided by the width of the class. In our example, with a class containing pitches between 30 and 34 meters, the width is 4 (because the interval is 4). For throws between 35 and 40 meters, the class width is 5..
Now suppose that 8 children have achieved results in the range of 30 to 34 meters. The class density would therefore be 2 (8 divided by the class width 4). In this way, a rectangle of width 4 and height 2 is created in the histogram. The observer of the graph can now read the number of entries from the height and width , since for this it is only necessary to multiply the two lengths of the songs.