Bullet charts were invented in 2005 by Stephen Few to replace the clunky gauge charts often found on dashboards. The basic purpose of a bullet chart is to present a quantitative measure along with the context around it that shows us how we should assess the measure – does the value meet a target? Is the measure good, satisfactory, or bad?
Bullet charts are composed of the following elements, illustrated in the image below:
Bullet charts are often used to compare current numbers against forecasts, or performance against targets for various metrics. They can also be used to compare past performance against current numbers in year-to-date comparisons or used with more than one comparative measure for multiple simultaneous comparisons.
Bullet charts provide a data-rich and efficient display of several measures. Their compactness makes them ideal to use in dashboards where several charts can be stacked in a relatively small area. This allows for individual assessment as well as quick comparison between metrics. Bullet charts not only give us the numbers in a concise manner, but they also provide context to help us understand the numbers.
One of the drawbacks of using a bullet chart is that they are not as familiar and intuitive to first-time users as a typical bar or a pie chart. This is one reason why gauge charts are still popular despite their heavy consumption of real estate on the screen.
Since the invention of the bullet chart, there have been many variations introduced, each of which can be used in a different context depending on the data structure and goal of the chart. Some of these variations are listed below.
A common variation on the horizontal bullet chart that we saw above is the vertical bullet chart, shown on the right below. As with bar charts, horizontal bullet charts are better for long category names that can be accommodated to the left of the bar. Vertical orientations are better for data which contains a natural order, such as age classes or time series information, that are best read from left to right.
Another variation on the bullet chart gives more prominence to the performance measure by encoding it using a wider bar, with the comparative measure relegated to the back in the form of an outline bar series. The comparative measure has less visual weight but is clearly visible, and a missed target is prominently visible with the comparative bar overtaking the performance bar. This is seen in the North and West regions in the chart below.
A simpler variation of the overlapped bar chart is shown below, which centers the performance measure as a thinner bar against a lighter bar showing the benchmark measure.
A relatively simple variation on the bullet chart is one that combines a bar chart (representing performance) against a target marker.
To make the above chart easier to interpret, the performance measure can also be shaded green or red according to whether the target has been met or missed. As shown below, the obvious visual cue makes it much easier for the reader to quickly scan a large number of categories.
In cases where we wish to begin the qualitative scale at a number other than zero, we may use a marker (X in the image below) to indicate the performance measure. Using a marker is a better choice in these cases, since bars are interpreted through their height and truncated bars give us a false sense of relative value.
As with the previous example, the performance markers can also be colored to help the user quickly understand which categories have performance exceeding the benchmarks.
Another variation on the bullet chart is the integrated variance bar. The variance indicator is used to showcase shortfall (in red) or excess (in green). In the chart below, let us look at the South region. Here the target of 55 has been exceeded by the value of 70, and the excess is highlighted in green. By contrast, the North region has fallen short of the target by a value of 20, and the shortfall is shaded in red.
This bullet chart recommended by IBCS (International Business Communication Standards) normalizes targets of all categories to 100% so that they are aligned together irrespective of magnitude. The green and red bars cue the users to the % variance based on achievement (green for overachievement, red for underachievement).
This bullet chart is typically recommended when you are presenting multiple KPIs of different magnitudes or units of measurements (UoM) as shown below. Normalizing the target measures means that we can make percentage evaluations of the difference between the target and actual, even when each KPI uses a different UoM. In the following chart, for example, we see that the average order size exceeded the target by 25%, while revenue missed the target by 20%.
While the following are strictly not different types of bullet charts, they are interesting variations of those presented above.
Bullet charts can also handle multiple comparative measures which can be indicated using markers of different shapes. The chart below shows the previous year’s value using a triangular marker and the target using a line marker. This way, we have a distinct visual indication of whether the target has been exceeded or not, and we may simultaneously make comparisons with the previous year’s value.
Another option to show two comparative measures is the overlapped integrated variance bar. This chart is similar to the integrated variance bar discussed above but adds an outlined bar representing the second comparative measure behind the integrated variance bar. In the case below, the second comparative measure is the previous year’s value, while the variance value is calculated as the difference between the current year’s value and the target.
Bullet charts can be used for positive and negative values. For example, the target for profits may be a certain value, but the company may accrue a loss, pushing the profit metric to the negative side, as seen below. Expenses can also be visualized as a bar that starts from zero and extends downwards (in a vertical bullet chart) or towards the left (in a horizontal bullet chart) to represent money that is spent by the company. Note the reverse gradation in the qualitative scale for the expenses chart below – the smaller the expenses bar, the better it is for the company. The gradation is thus lighter for smaller values and progresses to darker shades with higher expenses.
Nevertheless, this may not be a very intuitive representation to readers who may have trouble reading the chart in the reverse direction and understanding the reversal of the qualitative bands.
Some targets are not meant to be exceeded. For example, expenses and number of defects are metrics where it is better to fall short of the target. For these types of targets, it is recommended to reverse the grading on the comparison bands to indicate a difference in the type of target, or reverse the direction of the measure bar itself, as shown below.
Sometimes, we may want to evaluate our values against subjective criteria to understand the quality of performance, rather than against a specific numerical target or forecast. The marker indicating the target can be omitted in this case.
- By Hamsini Sukumar