Effects in plm are meaningless?

Question

In R, the plm function documentation of package plm, we can read about possibility of choose one of three effects individual , time , twoways . Why such exists if I can just pick model type which already specifies which effect to use? Eg 'within' model will only use individual and random will always pick twoways . To say more - for example pooling model by definition takes no effect (no time and no individual ) so choosing effect in this case is meaningless. What's the purpose of this additional input?

Answer 1

How do you come to this conclusion? The within model can be used with "individual", "time" or "twoways". You should see different results for your model coefficients, when choosing a different effect. Also, for example, when you use "time" or "twoways", you should be able to get the specific time effects via

summary(fixef(yourmodel,type = "level", effect="time")) .

(My plm package version is 2.2-4.)