UNIT 4: Scatter diagrams and correlation

Question 1

Key points for drawing a line of best fit

Answer 1

• Find the mean point
• Plot the mean point in a different colour with a +
• Line of best fit must go through the mean point
• Aim for an equal number of points either side of the line
• Doesn’t always need to go through the origin

Question 2

Positive Correlation

Answer 2

When an increase in one variable means an increase in the second variable

Question 3

Negative Correlation

Answer 3

When an increase in one variable means a decrease in the second variable

Question 4

No Correlation

Answer 4

When the two variables are not related

Question 5

Interpolation

Answer 5

Making a prediction INSIDE the data range

Question 6

Extrapolation

Answer 6

Making a predication OUTSIDE the data range

Question 7

Spearman’s Rank Correlation Coefficient

Answer 7

Numerical value between -1 and 1 which tells you how much in AGREEMENT two sets of RANKED data are

Question 8

Pearson’s correlation coefficient (product moment correlation coefficient)

Answer 8

Numerical value between -1 and 1 which tells you whether data has a LINEAR correlation

Question 9

Correlation and causation

Answer 9

Correlation does not imply causation.

Causation is when there is a direct link between the two variables

Question 10

Explanatory (Independent) Variable

Answer 10

x- axis.

Often it’s a variable you can control - or goes up in equal amounts.

Question 11

Response (Dependent) Variable

Answer 11

y-axis. Usually responds to the change in your explanatory variable