 Hi R users:

 I am using the plm package for linear panel data analysis but encountered the following message when I try plm function to estimate an random model with individual effect.

 data.re.ind <- plm(X.RETURN. ~ IOB + IOBS,data=E,model="random",effect = "individual")
 Error in swar(object, data, effect) :  the estimated variance of the individual effect is negative

 I have tried the other estimation methods ("walhus", "amemiya", "nerlove") in addition to method "swar" but it does not help.

 I have googled for answer but I have not found the solution yet. Actually this problem encountered by some users but still remains unsolved, I am afraid. Would some people help in this regard?

 Best regards,

Wei-han Liu

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