Reading Bar Charts and Histograms

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.

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Reading Values from a Bar Chart

The Y-Axis Scale

The y-axis shows the values. To read a bar's value:

1. Identify the top of the bar
2. Trace horizontally to the y-axis
3. Read the value

Dealing with Imprecise Readings

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.