Have attitudes toward investing in the stock market changed in recent
years as the growth of stocks has slowed? In 1995, a random sample of
100 adults that had investments in the stock market found that only 20
said they were investing for the long haul rather than to become rich
or make quick profits. A random sample of 100 adults that had
investments in the stock market in 2002 found that 36 were investing
for the long haul rather than to become rich or make quick profits.
Let p1 and p2 be the actual proportion of all adults with investments
in the stock market in 1995 and in 2002, respectively, that were
investing for the long haul.

A 99% confidence interval for p1-p2 is what?

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Clarification of Question by lingling1-ga on 30 May 2006 13:58 PDT

would it be -.157 +_0.062 (negative)
or
.157 +_0.062 (positive)

I think you could find some pretty good clues in whatever textbook you
are using for your class.

This is a simple confidence interval for comparing two proportions.
The frequentist answer is simply the difference in the two proportions
(.2 - .36 or -.16) +- (plus or minus) 2.054 * the pooled population
standard deviation [which by frequentist calculations is 2.054 * .0625
or 0.128]. I suspect however that the  difference you are interested
in would be p2 - p1,  which would have a CI of .032 to .288.    A
Baysian Interval would be slightly different but it isn't realy taught
in the schools so I'll not go there.

so Karlheinz-ga,
would it be -.157 +_0.062 (negative)
or
.157 +_0.062 (positive)