-ll(a) ul(b)- means that in a given observation, the observed response
can be anywhere between a and b. If it is actually smaller than a or
greater than b, it is actually truncated. -truncreg, ll(0)- would be
equivalent to the "standard" Tobit procedure: it says that anything at
zero or below, it is actually truncated at zero.
--
Stas Kolenikov
http://stas.kolenikov.name
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