Visualization is a key to success in regression analysis. This is one of the (many) reasons I am also suspicious when I read an article with a quantitative (econometric) analysis without any graph. Consider for instance the following dataset, obtai...

![What value is cross country GDP correlation? [Part One]](http://www.backsidesmack.com/wp-content/uploads/2011/05/now-gc1-1024x489.jpg)

Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).