Scatter-graphs How to produce, describe and interpret a scatter-graph - Correlation - Line of Best Fit

Positive correlation As one goes up... The other goes up

Negative correlation As one goes up... The other goes down

Perfect positive correlation Weak positive correlation No correlation Weak negative correlation

No correlation

Line of Best Fit “A line as close as possible to all points” How? 1) The line should have an equal number of points either side of it. 2)The line should go through the mean point (x-coordinate: mean of all x values, y-coordinate: mean of all y values) Optional

Line of Best Fit “A line as close as possible to all points” Why? The line can be used to predict values: Interpolation: Predicting values within the range covered. Extrapolation: Predicting values outside the range covered.

Line of Best Fit “Post hoc, ergo propter hoc” “After it, therefore because of it” Rarely true Just because two things are correlated doesn’t mean one causes the other.

Discuss “If you spend a lot of time on the phone, you have a better chance of ending up in a high-paying job” “The larger your shoe-size, the greater your bank overdraft” “Learning maths makes you a better musician”

Positive, Negative or None? Remember: correlation doesn’t mean one thing causes the other – it just means there is a relationship between them. Time spent travelling  Distance covered Level of education  Level of income Amount of clothing worn  Temperature outside Number of pages in a book  Copies sold Cost of car insurance  Age of driver Number of socks owned  Number of cars owned