Line graphs (Fig. 3.2) visually show continuous variables such as movements over time. They range from straightforward visual representations of trends to depictions of complex advanced statistical analyses.
Line graphs are probably the most popular of all graph styles in scientific writing. Unfortunately, studies have shown that many readers lack the skills to interpret them (Macdonald-Ross, 1977a). If you decide to use line graphs, keep them as simple as possible. Limit the number of lines in any one graph. Visually distinguish different lines by using different symbols, and label each line carefully.
Note that line graphs are appropriate only for continuous data. A false impression may be given if successive discontinuous data points on a graph are connected. It is better to present such information as a bar graph or to leave the points on the graph without connecting lines.
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