Hello everybody,

I am currently investigating the effects of a host country's domestic war on donor ODA payments in a dyadic dataset. My basic model has the following form:

ODA = war + population + oil + ... + slave fixed effects (all controll variables are logged and lagged by one year)

and now I want to further enhance the robustness of my results by adding different fixed effects.

Now the signs change with some control variables, e.g. In the above example, oil first entered into the model positively and becomes negative if I additionally control for annual fixed effects, while my independent variable remains significant.

For example, how can I explain this change of sign when adding fixed annual effects and / or donors fixed effects? What causes this? I'm really unexperienced in this field and would be very happy for any help.

Many thanks
Marco