The Line Predicts; the Points Happened

You'll learnto separate a point that happened from the line's prediction, and the gap between them.

A fit line predicts and the plotted points are what actually happened, so a prediction comes from substituting into the equation, never from reading a dot. Points leak in three places: reading a data point when the line was asked, misinterpreting the slope or intercept, and reporting an actual or predicted value when their difference was asked.

8 STEPS · 6 QUICK CHECKS · the line predicts · the gap is the residual · v2

points vs line

Before you start

What you're looking at

A scatterplot of plant height versus age: gray plotted points and a cyan line of best fit, y = 2x + 10.

The question

Does the item want an observed point, the line's prediction, or the difference between them?

Watch for

Watch the cyan line summarize the trend while single points sit above or below it.

What the symbols mean

Cyan is the fit line y = 2x + 10; gray dots are observations; axes are cm versus weeks.

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