Reading a scatter plot

Reading a scatter plot

Reading a scatter plot

A scatter plot draws one dot for each pair of measurements. The shape of the cloud of dots tells you how the two quantities are related.

The three kinds of association

  • Positive association — as one quantity goes up, the other tends to go up too; the dots rise from left to right.
  • Negative association — as one goes up, the other tends to go down; the dots fall from left to right.
  • No association — the dots are scattered with no clear direction.

Strength of the pattern

The closer the dots lie to a straight line, the stronger the association. A loose, wide cloud is a weak association even if it leans one way.

Outliers

A single dot far away from the rest is called an outlier. It does not break the overall pattern, but it is worth noticing and explaining.

Three rules that always help

  • Rising dots = positive, falling dots = negative, no direction = none.
  • Tighter to a line = stronger association.
  • Spot outliers, but judge the trend from the whole cloud.

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