Correlation, lines of best fit, outliers, interpolation and extrapolation, populations, samples and bias.
What you will learn
- Plot a scatter graph and describe the correlation
- Use a line of best fit to estimate, knowing when it is reliable
- Spot an outlier
- Explain the difference between a population and a sample, and why a sample may be biased
Correlation and the line of best fit
A scatter graph plots pairs of values.
If the points go up from left to right there is positive correlation; down, negative correlation; no pattern, no correlation. Describe it in context: "the longer students revised, the higher their marks tended to be."
A line of best fit is a straight line through the middle of the points, with about as many above it as below. Read an estimate from the line, not from the nearest point: go up from the value to the line, then across to the other axis, using the scale (check what one small square is worth). A point far from the pattern is an outlier: ignore it when you draw the line.
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Correlation and the line of best fit
- Inside the data, not beyond it
- Populations and samples
- Try it: First question
8 practice questions, marked as you go; about 25 minutes in all.
Key terms
Positive correlation, Negative correlation, No correlation, Population, Sample
In this unit: Statistics and charts
Averages and range, frequency tables, charts and diagrams, scatter graphs and sampling, and (Higher) cumulative frequency, box plots and histograms.
- Averages and range
- Frequency tables
- Charts and diagrams
- Scatter graphs and sampling
- Cumulative frequency, box plots and histograms