11.9: Summary

Visual summaries of data can be an extremely helpful aid in understanding the structure of observed data. In this chapter we presented a few of the most popular types of visual summaries that you are likely to encounter in the media and research papers. Bar charts are visual representations of frequency distributions where the height of the bars corresponds to the frequencies. Bar charts can also be used to compare means, medians, ranges, standard deviations, and other numerical summaries for a variable using at least an interval measurement scale. Pie charts are an alternative method for visually representing frequencies, though they are more difficult to interpret. Line graphs are used to show how the value of a variable changes over time or space. Line plots are characterized by connecting the consecutive plotted points by lines so that any trends can be easily visually observed. Histograms are visual representations of frequency distributions where the variable of interest is measured on a interval or ordinal scale. The range of the variables is divided into classes, and the frequencies are plotted as rectangles whose width corresponds to the width of the class and whose height corresponds to the frequency. Shapes of histograms are classified by the number of peaks, or modes, that occur. Unimodal histograms are classified by symmetry. Finally, scatter plots can be used to investigate associations and relationships between two variables that are measured on interval or ratio measurement scales. 

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