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...ta.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 [[al...

...ion, effect = c("individual", "time", "twoways"), model = c("within", "random", "ht", "between", "pooling", "fd"), random.method = c("swar", "walhus", "amemiya", "nerlove", "kinla"), inst.method = c("bvk", "baltagi"), index = NULL, ...) { nframe <- length(sys.calls()) is.a.list <- class(formula)[1] == "list" if (is.a.list) { plmlist <- match.call(expand.dots = FALSE) plmlist[[1]]...