Secondly I will use standard deviation to mean all the second hand price of the entire car make I have selected.
Ford
This graph is a negative correlation and shows that as the age the ford cars increases the second hand price goes down rapidly.
This graph is positive correlation and shows that as the engine size increases, the second hand price goes up by a small amount.
Vauxhall
This graph is a negative correlation and shows that as the age of the Vauxhall car increases the second hand price goes down
This graph is a positive correlation and shows that as the engine size increases the second hand price increases
Peugot
This graph is a negative correlation and shows that as the age of the Peugot car increases the second hand price goes down
This graph is positive correlation and shows that as the engine size increases, the second hand price goes up by a small amount.
Volkswagen
This graph is a negative correlation and shows that as the age of the Volkswagen car increases the second hand price goes down
This graph is positive correlation and shows that as the engine size increases, the second hand price goes up by a small fraction.
Rover
This graph is a negative correlation and shows that as the age of the rover car increases the second hand price goes down
This graph is a positive correlation and shows that as the engine size increases the second hand price increases.
Fiat
This graph is a negative correlation and shows that as the age of the rover car increases the second hand price goes down
This graph is a positive correlation and shows that as the engine size increases the second hand price increases.
Nissan
This graph is a negative correlation and shows that as the age of the rover car increases the second hand price goes down
This graph is a positive correlation and shows that as the engine size increases the second hand price increases.
Renault
This graph is a negative correlation and shows that as the age of the Renault car increases the second hand price goes down
I can see from those graphs that each make of cars had the same result for each factor. The engine size in all the make were all the same and as the age of the car got older the second hand price went down.
Standard deviation
I am going to use standard deviation because it measures the spread of the data about the mean valve. It is useful in comparing sets of data which may have the mean but a different range. For example, the mean of the following two is the same: 15, 15,15,14,16 and 2.7.14.22.30. However, the second is cleverly more spread out. If a set has a low standard deviation, the values are not spread out too much.
Standard deviation will give me me a more detailed picture of the way in which the data is dispersed about the mean as the centre of the distribution. Its main use is to compare two sets of data.