Final answer:
The statement is false; a legend is helpful for a double bar graph even when it has only two kinds of bars to clarify the data representation.
Step-by-step explanation:
The statement that a legend for a double bar graph is used to define the colors, symbols, or patterns of the content in the graph only when the graph has three or more kinds of bars is false. A legend is beneficial even when just two kinds of bars are used in a double bar graph. It provides clarity by indicating which bar corresponds to which set of data, which is crucial for accurately reading and interpreting the graph.