Hello,
Is there a clearcut answer as to why R prints 'NA' sometimes instead of
standard errors?


mle2(minuslogl = nlikfun4, start = list(a = 1, c = 1, d = 0.2,

b = 0.1, b1 = 0.1), method = "Nelder-Mead")

Coefficients:

Estimate Std. Error z value Pr(z)

a 3.83845751 0.47320236 8.1117 4.993e-16 ***

c 0.95545367 NA NA NA

d -0.22509015 NA NA NA

b 0.04260199 0.00743892 5.7269 1.023e-08 ***

b1 0.00212538 0.00031189 6.8145 9.459e-12 ***

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regards,

s

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