1. Scatter Diagrams
Objectives:
D Grade Draw a line of best fit
C Grade Interpret the line of best fit

2. When you are deciding how strong the correlation is you are
Scatter Diagrams
When you are deciding how strong the correlation is you are
imagining a straight line being formed by the points.
The line of best fit is exactly that: - the line that can be drawn
that will pass closest to as many points as possible
This is a graph of the number of calories and their fat content of different foods.
Note:
1200
1100
1000
900
800
700
600
500
400
300
200
100 X
Fat (g)
Calories
The line does not have to
start at the origin (0,0)
The line does not have to
pass through any points
all.
There is one point that
the line doesn’t go
anywhere near, this is an
‘outlier’, a value that
doesn’t fit the rest of the
data

3. Why might this point be an outlier?
Scatter Diagrams
Why might this point be an outlier?
The data could have been
incorrectly recorded.
1200
1100
1000
900
800
700
600
500
400
300
200
100 X
Fat (g)
Calories
It could be a food that is
made up of just fat and
sugar

4. When the line of best fit is marked an overlay is used to decide
Scatter Diagrams
When the line of best fit is marked an overlay is used to decide
whether it is a good line or not so be careful.
If your line appears outside
this it will be marked as
wrong.
1200
1100
1000
900
800
700
600
500
400
300
200
100 X
Fat (g)
Calories

5. The line of best fit can be used to make predictions.
Scatter Diagrams
The line of best fit can be used to make predictions.
If a food had a fat content
of 30g predict what how
many calories it would have.
1200
1100
1000
900
800
700
600
500
400
300
200
100 X
Fat (g)
Calories
You cannot use this to predict
a value that is outside the
range of data
For example you cannot use
it to predict the calories for a
food with a fat content of 80g
520
You would not use it to
predict the fat for over 700
calories because any outliers
do not fit in with the general
pattern of results

6. p39 Scatter Diagrams Worksheet Q3 Q4
The table shows the ages and arm spans of
seven students in a school. Q4
The table shows the ages and second-hand values
of seven cars.
Age (years) 16 13 10 18 15
Arm Span (inches) 62 57 59 64 55 61
Age of car (years) 2 1 4 7 10 9 8
Value of car (£)
4200
4700
2800
1900
400
1100
2100
Draw a scatter graph of the results
Describe the type and strength of correlation
Write a sentence explaining the relationship
between the two sets of data
Draw a scatter graph of the results
Describe the type and strength of correlation
Write a sentence explaining the relationship
between the two sets of data

7. Amount of rainfall (mm)
Scatter Diagrams
Worksheet Q5
The table shows the daily rainfall and the number
Of sunbeds sold at a resort on the south coast
Amount of rainfall (mm) 1 2 5 6 9 11
Number of sunbeds sold
380
320
340
210
220
110 60
Draw a scatter graph of the results
Describe the type and strength of correlation
Write a sentence explaining the relationship
between the two sets of data

8. p39 Scatter Diagrams Q3 Q4 1 2 3 4 5 6 7 8 9 11 10 Age of Car (years)X 68 66 64 62 60 58 56 54 52 50
Age (Years)
Arm Span (inches) 1 2 3 4 5 6 7 8 9 11 10
Age of Car (years)
Value of car (£)
1000
2000
3000
4000 X X X X X X X X X X X X X

9. Scatter Diagrams
400
350
300
250
200
150
100 50 Q5 X X X
Number of sun beds sold X X X X
Amount of rainfall (mm)