A graph places observations on chosen scales. Changing an axis can make the same differences look larger or smaller without changing the data. Describe the numbers and the pattern before making a claim. Two quantities changing together does not by itself show that one caused the other. A shared pattern is called an association. A graph alone does not prove a cause. Keep the same six points and change only the vertical-axis minimum. Check the numbers before judging the size of the change.
Engineering and scientific investigation · Discover & try
Which claims does a graph actually support?
Reading level 2 of 5 · DevelopingChange
Word help
Association
A tendency for quantities to vary together.
Axis range
The displayed minimum and maximum of a graph scale.
Watch · Try · Explain
See how it works
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Invented paired observations. Changing the axis scale changes appearance without changing the recorded values or the evidence.
What to look for
- The six observed values are51 through56.
- The same51–56 values occupy more height; the observations did not change.
- These points do not show a clear upward or downward pattern.
Explain what you noticed
In a hypothetical study, ice-cream sales and visitor numbers rise together. What does the graph alone establish?
Keep this idea: A graph’s appearance and an association are not, by themselves, proof of cause.
Follow the sources
- NIST/SEMATECH Engineering Statistics Handbook — Scatter Plot
- NIST/SEMATECH Engineering Statistics Handbook — Strong Positive Linear Correlation
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