Spearman’s Rank Correlation Coefficient A statistical technique to quantify the degree of relationship – correlation – between two sets of data
Stats and Geography <ul><li>You will be required to undertaken statistical analysis for your internal assessment (IA) </li></ul><ul><li>You do not need to be good at Maths to use them effectively </li></ul><ul><li>You must choose an appropriate and relevant technique </li></ul><ul><li>You must be accurate and follow all the steps carefully and methodically </li></ul><ul><li>You must carefully integrate the results of your statistical process into the analysis section of you write-up </li></ul>
Correlation <ul><li>Correlation assess the relationship between 2 sets of data in terms of the degree of similarity between the data sets. </li></ul><ul><li>As one set of values changes (increases for example) what does the other set of values do? </li></ul>
Spearman’s Rank Correlation Coefficient gives a numerical value (a quantity) to the degree of correlation between 2 sets of data
Step 1 <ul><li>Be clear about the hypothesis you are testing and the 2 variables being analysed (e.g. the higher the purchasing power of a country the lower the fertility rate) </li></ul><ul><li>Collect the data you need (a minimum of 10 pairs of values is required i.e you sample size should be 10) </li></ul>
Step 2 – The Table ∑ d 2 Australia Ecuador Taiwan Slovakia France USA China Ethiopia d 2 d Rank Fertility Rate Rank PP (US$) Country
Step 6 – Summarize the Results <ul><li>E.g. </li></ul><ul><li>With a Spearman’s Rank value of -0.83 I identified a strong negative correlation between purchasing power and fertility rates. The results were successfully tested for significance at both the 95% and 99% confidence levels thus I can conclude that the results are very reliable and did not occur by chance. These results therefore support the hypothesis that “the higher the purchasing power of a country the lower the fertility rate. The scatter graph of the same data (figure 1) further supports these conclusions. </li></ul><ul><li>These are the results I expected and can largely be explained in terms of levels of development. As a country develops …….. </li></ul>
The Pros – and Cons The Geofile handout (No 511 Jan 2006) – from which a large amount of this information comes – addresses the advantages and disadvantages of Spearman’s Rank. You should be doing the reading.