dear Alessandra,
although this list is not meant to do students' assignments, your
sincere admission deserves a friendly hand :-)
On the spot I can see two problems
- you must always fix the seed of the random number
generator to make sure you are always using the same numbers
(for instance, set seed 1234). If this is not clear have
a look at the way random numbers are generated, even Wikipedia
will do.
- to appreciate the effect of increasing
sample size you must compare estimates computed from N
observations and from a larger sample including those
observations plus some more. This is more easily done the
other way round: create a dataset, compute your stuff, throw
away some observations, compute same stuff, compare.
good luck!
Stefano
--
_________________________________________________________________________
Stefano Fachin
Professore Ordinario di Statistica Economica
Dip. di Scienze Statistiche
Università di Roma "La Sapienza"
P.le A. Moro 5 - 00185 Roma - Italia
Tel. +39-06-49910834
fax +39-06-49910072
web http://stefanofachin.site.uniroma1.it/