[R] Error: invalid type (closure) for the variable 'time' - object specific trend

[Tobias Christoph]

Hey,

I just have trouble adding a object specific time trend with the 
plm-package. I recieve the following error:
*
**"Error in model.frame.default(terms(formula, lhs = lhs, rhs = rhs, 
data = data,  : invalid type for the variable 'time' "*

I used the formula:

/ FE_trend<- plm(log(revenue) ~ log(supply)+ city*time, 
data=R_Test_log_Neu, model="within", effect = "twoways") //
/
Do you have an idea how to fix it?

Toby

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