Reading Line Graphs

Line graphs appear in approximately 1–2 of the 9 QR data sets. They typically show how a quantity changes over time, making them ideal for questions about trends, rates of change, and comparisons between time periods. This lesson covers reading values accurately, identifying trends, interpolating between data points, and comparing multiple lines.

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Reading Exact Values

Method

1. Find the point on the x-axis (e.g., "March" or "Week 5")
2. Move vertically up to the line
3. Move horizontally to the y-axis
4. Read the value

Dealing with Points Between Gridlines

Line graph values are often more precise than bar chart values because the data points are marked (with dots, crosses, or diamonds). If a point falls between gridlines:

• Determine the gap between adjacent gridlines (e.g., 50)
• Estimate the fraction of the gap (e.g., three-fifths of the way between 200 and 250 ≈ 230)

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Identifying Trends

Types of Trend