Scatter Graphs & Correlation
Describe simple mathematical relationships between two variables using scatter graphs, identify positive, negative, or no correlation, and use a line of best fit to make predictions
What a learner can do afterwards
- Plot bivariate data on a scatter graph and describe the type of correlation observed
- Draw a line of best fit by eye and use it to estimate a value within the data range
- Explain what positive, negative, and no correlation mean in the context of real data (e.g., temperature vs. ice-cream sales)
The lesson
A scatter graph shows how two things might be connected. Each point stands for one person or one item, plotted using two measurements at once, like hours of sleep and test score. You already know how to plot a point using an x-value and a y-value. A scatter graph just uses many of those points together to look for a pattern.
Priya asks eight classmates how many hours they revised and what score they got out of 20. She plots each classmate as one point: hours revised on the x-axis, score on the y-axis. Looking at all eight points, she sees them climb upward from left to right. That upward trend is called positive correlation. More revision tends to go with a higher score.
Correlation just describes the pattern in the points. Positive correlation means as one variable goes up, the other tends to go up too, like temperature and ice-cream sales. Negative correlation means as one goes up, the other tends to go down, like the age of a used car and its price. No correlation means there is no clear pattern at all, like shoe size and test scores.
A line of best fit is a straight line drawn by eye through the middle of the points, with roughly the same number above and below it. Use it to estimate values that sit inside the range of data you actually plotted. Predicting far outside that range is much less reliable, since you don't know if the pattern keeps going.
Points trending up mean positive correlation, points trending down mean negative correlation, scattered points mean no correlation, and a line of best fit predicts values in between.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.