Monday, 1 August 2016

HOW TO USE SPEARMAN’S RANK CORRELATION COEFFICIENT

Prediction
Always start with a prediction.  This is sometimes called a hypothesis.
If you plan to related amount of weathering to the age of the headstone, what is the hypothesis?  Write it down below.
The null hypothesis
Because you are carrying out a statistical test, it is best to follow mathematical conventions and add the null hypothesisThis always states that there is no relationship between the two variables.  This is done so that the Spearman’s Correlation Coefficient can disprove the null hypothesis in order to show that your hypothesis (or prediction) is more likely to be true and is not due to chance.
Write down the null hypothesis.
Scatter graph:
The next stage is to draw a scatter graph to show the data you have collected.  This will show you roughly the relationship between the two sets of data.
The scatter graph shows two patterns about the data:
POSITIVE OR NEGATIVE RELATIONSHIP: 
It shows whether there is a positive or negative relationship between the two sets of data.  This is shown by the sign (+ or -), which is part of the Rs value that you are going to calculate, and also by the direction in which the points on the scattergraph lie.
1)  If one set of data increases as the other increases, this relationship is POSITIVE
 2) If one set of data decreases as the other increases, this relationship is NEGATIVE.
 3) If there is no apparent relationship between the two sets of data, the scatter graph is RANDOM.
 STRENGTH OF THE RELATIONSHIP 

It shows how closely related the two sets of data are.  This is given by how close the points on the scatter graph are to the line of best fit and also by the Rs value that you are going to calculate.  Draw the line of best fit on the scatter graphs below and say which one shows the closest relationship between the two sets of data.

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