1. Scatter Graphs Finding the equation of the line of best fit
GCSE Statistics
Scatter Graphs
Finding the equation of the line of best fit

2. Using a line of best fit
there are a couple of terms used in the statistics GCSE that are not used in Unit 1
Interpolation – this is when the data point you need lies within the range of the given data values
- this gives fairly reasonable estimates
Extrapolation – this is when the data point you need is outside the range of given data values
- this gives unreliable estimates

3. Equation of a line of best fit
This is the same as the equation of any straight line in that it takes the form y=mx + c
Also written (for some reason) y = ax + b
Where
a (or m) is the gradient change in x change in y
b is the value of y when x = 0 (the intercept)
if you use a false origin you can not read b from your graph
if b can not be read from the graph, put the value of a into the equation and the coordinates of a point on the line, then solve the equation to find b

7. Interpreting the gradient a and the intercept b
the gradient here is =0.5
in context this means
the cost for each mile travelled is £0.50
the intercept is £1.85
in context this is the standing charge the taxi driver has

8. Your turn
Exercise 5F page 189