Pie graphs (or pie charts, or circle diagrams) represent relative frequency or percentage distributions with circles divided into sectors that are proportional in areas to the relative frequency or percentage values. If there is an ordering to the categories (or classes) of the distribution, it is typically preserved in a clockwise sequence starting at the 12 o’clock position. We now list out some of the merits and demerits of pie graphs over other ways of data visualization.
Advantages of Pie Charts:
- The pie chart is visually striking and easy to understand.
- The pie chart gives us an idea of the relative proportion for each category of data at a single glance.
- Pie charts are frequently used in presentations and marketing research to express the raw data in visual form.
- Pie charts are the best way to represent percentage breakdowns. For example, we can represent the budget of a family by a pie chart by dividing it into categories such as food expenses, education, utilities, savings, etc.
- Pie charts are easier to read for a statistically untrained person compared to bar charts and histograms.
- Pie charts can allow us to easily make rough comparisons amond different categories. For example, if one of the slices of the chart occupies roughly half of the area of the circle we can conclude that that category represents about 50% of the total without knowing the absolute frequency of that category.
Disadvantages of Pie Charts:
- Pie charts are less useful than bar graphs for accuarate reading and interpretation when the series is divided into a large number of components or the difference among the components is very small.
- If the given data has more than six categories the pie chart becomes very crowded and ugly. In such cases it is not advisable to use pie charts to represent the data.
- If most of the sectors of the data are of roughly equal size then we cannot make visual comparisons between categories by simply looking at the pie chart.
- Before drawing the pie chart, we need to do calculations of central angles for each category. These calculations are boring and tedious. On the other hand, no calculations are needed in order to draw simple bar graphs, line graphs, etc.
- Pie charts cannot be used to represent time series data.
- We cannot make comparisons between two sets of data with the help of a single pie chart. On the other hand we can draw two bars for each category to visually represent two sets of data in a single bar graph.
- Circles are difficult to compare and thus pie charts are not very popular among professional statisticians.