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Solution to Exercise 3.3.1.

As mentioned in class, the problem needs to be restated. Let tex2html_wrap_inline618 , tex2html_wrap_inline620 be independent Bernoulli random variables with success probability tex2html_wrap_inline622 , and put tex2html_wrap_inline624 = tex2html_wrap_inline628 , tex2html_wrap_inline638 = tex2html_wrap_inline768 . Assume

(i)

  equation344

(ii)

  equation350

Then

  equation356

Actually, since tex2html_wrap_inline638 tex2html_wrap_inline772 tex2html_wrap_inline774 we have tex2html_wrap_inline776 and of course tex2html_wrap_inline778 tex2html_wrap_inline780 1, so in fact condition (i) implies condition (ii), and the latter is unnecessary.

We will apply the Lindeberg CLT given in class. That is stated as follows:

  theorem365

We will use our triangular array of Bernoulli random variables, where tex2html_wrap_inline820 . Conditions (I), (II), and (IV) hold immediately. Of course, (III) and (V) are achieved by centering and normalizing: define

  equation390

which is the variance of the row sum tex2html_wrap_inline822 . Then put

  equation398

Then (III) and (V) hold. Thus, we only need to do any work to verify the Lindeberg condition, condition (VI). Now the event tex2html_wrap_inline824 in the Lindeberg condition is the same as

  equation406

But tex2html_wrap_inline826 only takes on the values 0 and 1, and tex2html_wrap_inline832 is between 0 and 1, so

  equation413

However, tex2html_wrap_inline838 (condition (i) in the problem), so for each tex2html_wrap_inline840 there is an tex2html_wrap_inline698 such that for all tex2html_wrap_inline700 , tex2html_wrap_inline846 , i.e. for all tex2html_wrap_inline700 , tex2html_wrap_inline850 and hence by (38) the event in (37) is empty. Thus, the indicator inside the expectation in (34) is 0 and so for all tex2html_wrap_inline700 ,

  equation422

We see then that all the conditions in the Lindeberg theorem hold, so tex2html_wrap_inline856 . Observe that tex2html_wrap_inline858 is the l.h.s. of (33), and the problem is done.



Dennis Cox
Mon Oct 13 13:28:22 CDT 1997