R help - Jun 2012 - How can I choose the link function in function 'gam' in MGCV packages?

Hi,Dear R users,
 I am studying the generalized additive model and employ the 'mgcv'
packages
 in R.For example,I want to conduct the empirical study.The dependent variable 
 is GDP and the independent variable is foreign direct investment.How can I
choose
 the best link function and the family in this situation?
  
 In addtion, could anyone know how to interpret the figures in the gam.check
function?
 The first fig is Q-Q plot,but the other?
  
  
 Thanks in advance
  
 wanhai
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