Is Pearsons Product Moment Correlation Coefficient the same as Spearmans Rank Correlation Coefficient?
No, they are not the same. Pearson’s only tries to measure if there is a LINEAR relationship between the two variables, whereas Spearmans looks to see if there is a tendency for y to increase (or decrease) as x increases, whether the relationship is linear or otherwise. Because of this, you may well end up with quite different values for the two coefficients – if the two variables have a perfect quadratic (say) relationship then Spearmans would give a coefficient of 1 (or -1) but Pearson could be close to 0 as the points would not fit well to a straight line. There is also the issue of whether your data is objective/subjective/ranked to decide which measure is more appropriate, as mentioned by the previous answerer.
