Question

1.Are there circumstances in which a pie chart cannot be drawn, but a bar graph could be drawn? If so, what are these circumstances and give examples.

2. when is a pie chart or bar chart preferred over the other one?

Answer 1

BAR CHART

A bar chart represents data using a series of bars across two axes. The x-axis (the horizontal) classifies the data by group, with one bar for each group. So for example, if you were displaying the number of beads of each color in a jar, the x-axis would have a section for each color, and each color would have its own bar. The y-axis (the vertical) shows the value for the category for each bar. In the bead example, this would be the number of beads. So the bar for green beads might extend up to five, for example, whereas the bar for red beads may extend up to only two. The y-axis can be many different values, though; for example, money, a growth rate, an average speed or even a percentage of the whole. Similarly, the x-axis values and bars could represent the same quantity at different points in time, and this capability shows a big difference between bar graphs and pie charts.

PIE CHART

Pie charts are circular graphs that display percentages of a whole as if they were slices of a pie. This is very similar to bar graphs in that the individual slices of pie mean that the data has to have the potential to be categorized. The “slices” of the pie have sizes to indicate the proportion of the whole they represent (although a legend beside the chart usually shows the precise figures), but unlike bar graphs, pie charts can’t be used to explicitly show absolute number values for each group. The shape is the most obvious difference between pie charts and bar graphs, but the restriction to proportions with pie charts is the most important

Both the bar chart and pie chart are common choices when it comes to plotting numeric values against categorical labels.

1. A pie chart cannot be drawn if the data do not include all possible values of the qualitative variable.

For Example-  taking the average of a metric (e.g. average spend by user type) or if we look at proportions that are independent (e.g. proportion of survey respondents who use each of the polled apps). A bar chart is fine for this case, but a pie chart falls short. Since the circular shape implies that slices are parts of a whole, it is too easy for a reader to mistake a sum of slices as a representative of some sort of total.

Pie charts are best to use when you are trying to compare parts of a whole. They do not show changes over time. Bar graphs are used to compare things between different groups or to track changes over time. However, when trying to measure change over time, bar graphs are best when the changes are larger. If there are too many slices, then it’ll probably run into the problem of either there being similarly-sized slices or slices that are too small. Those small slices can be difficult to read and color distinctly.

A pie chart can only be used if the sum of the individual parts add up to a meaningful whole, and is built for visualizing how each part contributes to that whole. Meanwhile, a bar chart can be used for a broader range of data types, not just for breaking down a whole into components.

2. A bar chart is preferred when trying to compare two specific values .For example, if you were showing the results for a class president election in school, each candidate would have his or her own bar on the x-axis and the values on the y-axis would be number of votes the candidate received and for example if you were showing the revenues of various companies, you could use a bar chart with a bar for each company and the length corresponding to its revenue in dollars. In both of these cases, you can easily see at a glance the category (in the examples, the candidate or company) that has the highest value (in votes or dollars, in the example), and the graph conveys the main information in a straightforward and easy-to-interpret fashion.

Pie charts are helpful for comparing parts of a whole.you can use pie charts when the proportions are important in your data and especially if the proportions are substantially different. If you have a specific point to make – for example, showing that a certain household expense makes up over half of your outgoings – then a pie chart can be the best way to do so clearly.a pie chart works well for displaying a breakdown of sales for each item for a business. Your total sales are the whole “pie,” but the slices tell you how much each product contributes. The one major benefit to the pie chart is that it immediately sells the idea of a part-to-whole comparison. With a bar chart, it may not be immediately clear how much each bar contributes to the whole, or that it’s the kind of comparison that is of interest, unless the bar units are in terms of proportions or percentages.