A student investigated the relationship between the concentration of dissolved copper (in mg dm−3\text{in mg dm}^{-3}in mg dm−3) in a river and the rate of respiration of a bacterial species (measured in μg O2 h−1 g−1\text{measured in } \mu\text{g O}_2\text{ h}^{-1}\text{ g}^{-1}measured in μg O2 h−1 g−1 of dry mass) across 12 different sampling sites.
Which of the following is the correct procedure for the statistical analysis of the data collected by the student?
Calculate the mean of both variables across all 12 sites and perform an unpaired Student's t-test.
Group the sites into 'polluted' and 'unpolluted' categories, find the frequencies of bacteria in each, and perform a chi-squared test.
Rank the values for both copper concentration and bacterial respiration rate across the sites, and calculate Spearman's rank correlation coefficient.
Order the sites by copper concentration, calculate the differences in respiration rate between successive sites, and perform a paired t-test.
