Creating and Interpreting Scatter Plots

Pre-Algebra · Axiom Academy

Turn a list of paired measurements into a picture, and let the cloud of points tell you how two quantities move together. Eight students reported how many hours they studied and the test score they earned. Every student is one ordered pair (x, y) — and a scatter plot just drops each pair at the spot x across, y up. Each row of the table is one point on the grid 2. The Direction the Cloud Leans Once the points are down, the first thing to read is direction . Drawing a straight line of best fit through the middle of the cloud makes it obvious: does the line tilt up or down as you move right? As x increases, y tends to increase. More hours studied → higher score. The fit line slopes upward . As x increases, y tends to decrease. Warmer days → fewer cups of hot cocoa sold. The fit line slopes downward . Left: study hours vs score climb together. Right: outdoor temperature vs hot-cocoa cups fall as one rises. Same idea, opposite tilt — and a cloud with no tilt at all would mean no correlation . 3. The Strength of the Pattern Direction tells you which way ; strength tells you how reliably . Strength is just how tightly the points hug the line of fit: cling to it and the correlation is strong ; scatter far from it and it's weak — even when both clouds lean the same way. Points sit almost on the line. Knowing x predicts y well. Points are widely scattered. The trend is real but a single x tells you little.

This is the written version of the interactive lesson above. See the full Pre-Algebra course.