You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
Bar charts appear in approximately 2–3 of the 9 QR data sets. They test your ability to read values from a visual scale, compare quantities, and perform calculations using the data you extract. This lesson covers standard bar charts, grouped (clustered) bar charts, stacked bar charts, and the key differences between bar charts and histograms.
The y-axis shows the values. To read a bar's value:
Bar charts in QR are often drawn so that bars do not land exactly on gridlines. You may need to estimate.
Example: If the gridlines are at 0, 50, 100, 150, 200, and a bar's top is roughly three-quarters of the way between 100 and 150, the value is approximately 135.
Tip: The answer options will accommodate the imprecision. If the options are 125, 135, 145, and 155, you need to read the bar to the nearest 10. If the options are 130, 132, 134, and 136, the chart would have finer gridlines.
| Pitfall | How to Avoid It |
|---|---|
| Y-axis does not start at zero | Check the bottom of the y-axis. A broken axis exaggerates differences. |
| Unclear gridlines | Count gridlines carefully. If the y-axis goes from 0 to 500 with 5 gridlines, each gap is 100. |
| Different scales on left and right | Some charts have two y-axes. Check which bars correspond to which axis. |
Grouped bar charts show multiple bars side by side for each category, distinguished by colour or pattern.
Example: Sales by quarter for three products. Each quarter has three bars (one per product), grouped together.
Stacked bar charts show bars divided into segments, one on top of another. The total height represents the overall total, and each segment represents a component.
To find the value of an individual segment:
Example: A stacked bar has three segments. The total bar reaches 450. The bottom segment goes from 0 to 180 (value: 180). The middle segment goes from 180 to 310 (value: 310 − 180 = 130). The top segment goes from 310 to 450 (value: 450 − 310 = 140).
Common Error: Reading the top of a middle segment as its value. If the middle segment ends at 310, its value is not 310 — it is 310 minus the starting point (180), giving 130.
In a bar chart, the bars represent categories (e.g., products, regions). There are gaps between bars.
In a histogram, the bars represent continuous ranges (e.g., age ranges, weight ranges). There are no gaps between bars, and the area of each bar (not just the height) represents the frequency.
If all bars have equal width, the height represents the frequency, just like a bar chart.
Subscribe to continue reading
Get full access to this lesson and all 10 lessons in this course.