(a)[5]
Describe a way that could be used to estimate the population size of a mobile animal, for example a brown rat.
(b(i))[2]
The statistical test Spearman’s rank correlation ($r_s$) was used to determine whether altitude and the mean height of the soft rush plants were related. The formula for Spearman’s rank correlation is: $ r_s = 1 - \left( \frac{6 \times \Sigma D^2}{n^3 - n} \right) $ $\Sigma D^2$ means the total of the differences between the ranks of the two samples, and $n$ is the sample number. For this investigation, $\Sigma D^2 = 164$. Calculate the value of $r_s$. Show your working and give your answer to two decimal places.
(b(ii))[2]
Use your value for $r_s$ to evaluate the relationship between altitude and the mean height of the soft rush plants.