① Reading a scatter graphNo calculator
Each point shows two measurements. Read across and up carefully using the grid lines.
② CorrelationNo calculator
Describe the pattern: points going up (positive), going down (negative) or with no pattern (none).
③ Line of best fitNo calculator
A line of best fit passes through the middle of the points and can be used to make estimates.
④ Reliable estimatesNo calculator
Estimates inside the range of the data are more reliable than estimates outside it.
Key steps
Positive correlation: as one value increases, the other tends to increase.
Negative correlation: as one value increases, the other tends to decrease.
Line of best fit: draw a straight line through the middle of the points, with about as many points above it as below it. To make an estimate, go up from the horizontal axis to the line, then across to the vertical axis (or the other way round).
Equation of the line: read where the line crosses the vertical axis (this is \(c\)), then find the gradient \(m=\dfrac{\text{change up}}{\text{change across}}\) using two points on the line.
Reliable? Only trust estimates for values inside the range of the data you have.