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 Subject: statistics Category: Science > Math Asked by: lingling1-ga List Price: \$2.50 Posted: 25 May 2006 11:06 PDT Expires: 31 May 2006 14:18 PDT Question ID: 732341
 ```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?``` 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)```
 There is no answer at this time.

 ```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)```