spearman's rank

Question 1

what does spearmans rank correlation do

Answer 1

determines whether there is correlation between variables that dont show a normal distribution.

Question 2

what is the method to work out spearmans rank

Answer 2

Step 1: Rank each set of data (rank 1 being the smallest data figure)

Step 2: Find the difference in rank between the two species–> D

Step 3: Square the difference in rank, D^2

step 4: find the sum of D

Step 5: Substitute the appropriate numbers into the equation

Step 6: Refer to a table that relates values of r to probability. Look for the 0.05

Question 3

the equation for spearmans rank

Answer 3

r= 1- (6xsumofD^2)
—————-
(n^2-n)

where r is spearmans rank co efficient
D is the difference in rank
N is the number of samples.

Question 4

whats the rule for the value of r

Answer 4

if it is greater than the critical value for the number of samples in the data at the 0.05 probability level then the null hypothesis can be rejected. this means there is a correlation between the 2 variables.

EXAMINAR TIP- just because there is a correlation between the abundance of species A and B, it does not mean that the presence of species A causes the presence of species B