Pictographs

A pictograph uses picture symbols to convey the meaning of statistical information. Pictographs should be used carefully because the graphs may, either accidentally or deliberately, misrepresent the data. This is why a graph should be visually accurate.

Figure 1. Number of students who like chocolate chip cookies best

Figure 1 shows a scale that represents the number of elementary students who prefer chocolate chip cookies. This type of pictograph shows how a symbol can be designed to represent data. One cookie symbol represents two students, and a half-cookie image is used to represent one student. These data could have been easily presented in a histogram where the figure is expressed using a scale rather than a symbol.

Now let us look at another example of a pictograph.

Figure 2. Purchasing power of the Canadian dollar, 1980 to 2000

Figure 2 shows how the Canadian dollar shrank to a value of 46.17 cents over 20 years because of inflation. This information means the value of the 2000 Canadian dollar was worth less than half as much as it was in 1980! What is the problem with the depiction of statistics in this pictograph?

The size or area (total surface) of the dollars coin (loonie) graphic is misleading. The dollar value differences represented are exaggerated by the pictures. The graphics should reflect the actual purchasing power of the dollar of the year in question. Since 46 cents is just under half of one dollar, the 2000 loonie should appear to be just under half the size of the 1980 loonie. Instead of being one-quarter of the size of the 1980 loonie, the 2000 loonie should be about twice as big as is shown.

You may argue that people do not notice this misrepresentation when they look at a pictograph such as this one, and thus it is not particularly important. The fact is that subconsciously many people interpret the Canadian dollar to have lost far more of its value than it has in reality. Since many people use statistical information in making decisions, accuracy is important. In this case, the shrinking value of the Canadian dollar can affect people's perception about their ability to save money or their confidence in the Canada's economy.

If not drawn carefully, pictographs can be inaccurate. Statistics Canada rarely uses pictographs to release statistical information, but the media uses them quite frequently.