3 ms·
> In probability theory, the central limit theorem (CLT) states that, given certain conditions, the mean of a sufficiently large number of independent random va
by graycat 13y ago
> In probability theory, the central limit theorem (CLT) states that, given certain conditions, the mean of a sufficiently large number of independent random variables, each with a well-defined mean and well-defined variance, will be approximately normally distributed (i.i.d.).
No, that's just wrong. The context is some positive
integer n and values of some n real valued
random variables independent and identically distributed
(i.i.d.).
If for some n do what the quote says, then
are not guaranteed to
get a Gaussian.
Moreover, if do what the quote says and take the limit
as n goes to positive infinity, then, say, in the case
the random variables have expectation that is finite and finite
variance, will get
just the common expectation of those random variables --
this is the law of large numbers, not the
central limit theorem. That the distribution
of the mean
converges to the point with the expectation is
the 'weak' law of large numbers. That the
mean
converges to
the expectation with probability 1 is the
strong law of large numbers.
For the central limit theorem, add up the n i.i.d.
values and divide by the square root of n.
Then under meager assumptions (e.g., i.i.d. and,
for likely the strongest conditions known,
the Lindeberg-Feller conditions), as n goes to infinity, the distribution of the result will converge to
a Gaussian ('normal') distribution. Authors with
the details include J. Neveu, L. Breiman, M.
Loeve, and K. Chung.
It's essential to divide by the square root of
n, not just n.