Interesting that both John Lexmark (publicly) and Brian Vuong
(privately) sent identical pairs of e-mails.
On Wed, 31 May 2000, John Lexmark wrote, inter alia:
> I used Comparing Two Proportions to test, but someone told me that my
> P-value does not look right.
Would "someone" be your instructor, or a fellow-student, or an amicus
curiae of some sort, or ... ?
> Please tell show me where the mistakes are
>
> Phat= 2/50 = 0.04
>
> z= (.04-.10)/(/sqrt((0.10 * 0.9)/50)= -1.41
>
> p-value = (1- 0.0808) = 0.9192
I see you haven't answered "While we're about it, what textbook are you
using in class?", let alone what section(s) or page(s) therein you're
referring to. Your arithmetic appears to be correct, to the precision
that you report; your table lookup is less precise than your
arithmetic, but that may reflect the particular table(s) available to
you (it also may reflect sloppiness in the lookup).
You also have not identified particular parts of the original post that
were sticking-points (except by "someone"'s comment [I], perhaps).
What do you understand the "P-value" to be the p-value OF ?
If you cannot answer this question, better study the text some more.
Better yet, talk to your instructor, who REALLY needs to know that this
concept needs attention. THEN study the text some more.
If you _can_ answer it, and relate it to the problem that was set,
you should have no difficulty with the problem.
> > > An inspector inspects large truckloads of potatoes to determine the
> > > proportion p in the shipment with major defects prior to using the
> > > potatoes to make potato chips. [A]
> > > Unless there is clear evidence that this proportion is less than
> > > 0.10 she will reject the shipment. [B]
> > > To reach a decision she will test the hypotheses [C]
> > >
> > > H0: p=0.10, Ha: p<0.10 [D]
> > >
> > > Using the large sample test for a population proportion. [E]
> > > To do so, she selects an SRS of 50 potatoes [F]
> > > from the more than 2000 potatoes on the truck. [G]
> > > Suppose that only 2 of potatoes sampled are found to have major
> > > defects. [H]
> > > Determine the P-value of her test. [I]
I agree with Robert Dawson about the phrasing of the problem, and a
certain part is stated, in my view, imprecisely at best. This is however
a terminological quibble and does not affect the calculations that are
required.
-- DFB.
------------------------------------------------------------------------
Donald F. Burrill [EMAIL PROTECTED]
348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED]
MSC #29, Plymouth, NH 03264 603-535-2597
184 Nashua Road, Bedford, NH 03110 603-471-7128
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