I'm currently reading Maths and Stats for Web Analytics and Conversion Optimisation by Himanshu Sharma and noticed the following regarding regression analysis:
"If there is no or weak linear relationship between two variables or in other words the correlation between the two variables is zero or weak then this relationship is not good enough to predict anything. Therefore there is no point in running regression analysis."
This strikes me as ignoring non-linear regression analysis. I could understand if the last sentence was "Therefore there is no point in running linear regression analysis" but the author excludes all forms of regression.
My question is, even if the R is low, if you chart the data and see a curved scatter plot, should you be looking to run non-linear regression analysis as opposed to scrapping analysis entirely?
It is implied the R calc is Pearson's.