Barcelona Field Studies Centre

Priorat: Hypothesis Testing

The relationship between population size and the number of restaurants or wine cellars in each of the Priorat study villages can be presented as a scattergraph and tested using Spearman's Rank Correlation Coefficient.


Scattergraph to show the relationship between Priorat village population size and the number of restaurants

 

Scattergraph to show the relationship between Priorat village population size and the number of wine cellars

 


Restaurants and Wine Cellars in Priorat

Village Population Rank Pop Restaurants Rank Rest  d˛  Cellars Rank Cell  d˛ 
Pradell 169   1     1 1  
Gratallops 253   5     18 18  
Lloar 113   1     0 0  
Torroja 147   1     8 8  
Porrera 477   2     14 14  
S      

  • Calculate the coefficient (r˛) using the formula below. The answer will always be between 1.0 (a perfect positive correlation) and -1.0 (a perfect negative correlation).

When written in mathematical notation the Spearman Rank formula looks like this :


Spearman Rank Formula

 

A number of further relationships may be explored from population and services data, including the positive correlation between the percentage born in the rest of Spain and the number of wine cellars found in each Priorat town.