Positive correlation

 

If both sets of data increase (eg. shoe size increases with age), on a scattergram, the points will appear to go upwards from left to right.  The diagram below shows strong positive correlation.

 

 

Negative correlation

 

If one set of data increases whilst the other set decreases (eg. length of journey compared with the amount of petrol left in the petrol tank), on a scattergram, the points will appear to go downwards from left to right.  The diagram below shows weak negative correlation.

 

 

NB:       Remember that both positive and negative correlations can vary between no correlation through strong correlation to perfect correlation.