4.3)  Significance for correlation

To determine the radius of detectable pollution around a coal-fired power-plant and determine if this pollution will make it into the food-chain, samples of soil and spinach have been collected in 6 transects away from such a plant (spinach just loves heavy metals!). The compositional data are given in the separate datafile. You are asked to evaluate these data using the following statistical tools:

A. Plot the compositional data against distance for each transect. If the maximum allowable concentration is 0.35 ppm, what would be the minimum safe distance to grow spinach here?

B. What is the distribution of each dataset (use PAST)? 
	If you encounter log-normality: take the appropriate measures. 
	If you find multi-modality: split the dataset and continue with these various 	groups. Can you explain any multi-modality you may encounter?

C. Determine the correlation coefficient for each transect between soil and spinach composition (Pearson or Spearman will depend on your analysis at B)

D. Determine whether the correlation coefficients are significant at the 5% and 2.5% confidence levels (using tables 2.4 or 2.10 in Swan and Sandilands or the t-tables linked from the course website)

E. What are your conclusions?