Correlation describes the pattern
Points trending up to the right = positive correlation; down to the right = negative; no pattern = none. Strong vs weak describes how close the points lie to a line.
The line of best fit balances the points
Draw a single straight line with roughly equal numbers of points above and below; it should follow the trend and pass near the mean point. Use it to estimate one variable from the other.
Correlation is not causation
A correlation between two variables does not prove that one causes the other — there may be a third factor.
Drawn from real examiner reports.
Plotting the points but not drawing the line
Marking all the points correctly yet failing to draw the line of best fit through them.
A line that does not span the data
Drawing the line too short, or in the wrong place / wrong gradient, so it is not extended across the full range of the data.
Trusting predictions far outside the data
Reading a value off the line well beyond the plotted range (extrapolation) is unreliable — the trend may not continue.
Estimate by drawing lines from the axis to the line
To predict, draw a line from the known value up/across to the line of best fit, then read off the other axis; show these construction lines.
A scatter graph plots paired data to reveal a relationship:
"Strong" or "weak" describes how tightly the points cluster around a straight line. Correlation does not prove causation.
Points trending down to the right show what correlation?
A scatter graph of daily ice-cream sales against temperature shows points that rise from the bottom-left to the top-right. Describe the correlation, and say what it suggests.
