# ## Graph Data

If a collection of data contains only a few numbers, then there is little need to organize the numbers in order to analyze the data. When there is a large number of numbers in a collection of data, it becomes important to organize the data in a meaningful way to make analysis easier. Notice that the word data is the plural of datum. A collection of numbers or data is also called a data set.

Organizing data in stem-and-leaf plots, double bar graphs, frequency tables, histograms, line plots, and line graphs makes data easier to understand and to use.

When data are displayed, clusters, gaps, and outliers may be seen. A cluster is formed when several data points lie in a small interval. A gap is an interval that contains no data. An outlier has a value that is much greater than or much less than other data in the set. Such features are easily seen when the data are shown on a stem-and-leaf plot or on a line plot.

A histogram is a graph that uses bars to display how frequently data occur within equal intervals. A histogram looks like a bar graph but has no space between the bars.

Bar Graphs
A bar graph is used to display data when the data can be counted and you want to make comparisons. A vertical bar graph has a horizontal scale which names the items being counted. A vertical scale, at the left, shows the number counted. For example, snacks chosen by children as being their favorite may be listed along the horizontal scale. The vertical line may be numbered 0, 1, 2, 3, 4, and 5. The lengths of the bars would represent the numbers of children that chose a particular snack. On a horizontal bar graph, the locations of the scales are reversed. Teaching Model 7.4: Choose an Appropriate Graph