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If you study more hours for an exam, your score usually climbs. But as you use your phone throughout the day, your battery percentage drops.
When two measurable quantities change together in a recognizable pattern, we say there is an association between them.
How do mathematicians describe the path these dots follow?

Reading the Direction

Just like reading a sentence from left to right, always read a scatter plot from left to right along the horizontal xx-axis.
If the dots rise as you move to the right, that is a positive association — as the xx-variable increases, the yy-variable tends to increase too.
If the dots fall as you move to the right, that is a negative association — as the xx-variable increases, the yy-variable tends to decrease.
This rule connects directly to slope: an uphill trend has a positive slope, while a downhill trend has a negative slope.
What if two plots both drift upward, but one looks like a neat line while the other looks like a messy swarm of bees?

Measuring the Strength

When the points on a scatter plot settle along a straight line path, we call it a linear association.