st: FIXED EFFECTS VS FIRST-DIFFERENCING

[Paul Ngobo <Paul.Ngobo@univ-angers.fr>]

Can someone please tell me when to adopt a first differencing estimation 
and when to adopt a fixed effects estimation? I am estimating a model over 
9 years with multiplicative effects of the independent variables. While the 
IV-FE estimation does not yield many significant coefficients, the IV-FD 
does. So I wonder if there is a technique (like the HAUSMAN TEST) that 
could allow me to select one of these estimation methods?
Many thanks in advance
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