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# S2 Hypothesis Tests question... help! watch

1. Hi, I've done this and I get a very near answer, but it's not right! Can someone please show me how to do it, with working? (I promise this isn't from wednesdays paper )

The probability of Brand A lotion curing a particular skin complaint is 0.35 . It is thought that a new lotion Brand B will improve the cure rate. Brand B lotion was tested on 20 people. How many of the 20 people tested would need to be cured before the results would be significant at the 5% level?

Thank you to anyone who does this
2. I am sure the answer is 12! the book says 11!
3. Yep i got 12 too,

x~b(20,0.35)

p(x<c-1)>0.95 (the signs are equal as well)
hence c = 12
4. http://www.mathsnet.net/asa2/modules/s24criticalb.html

Mathsnet gets 11 I believe.
5. (Original post by ZJuwelH)
http://www.mathsnet.net/asa2/modules/s24criticalb.html

Mathsnet gets 11 I believe.
It does? Can you explain?
When I put n=20 x=11 and p=0.35, it tells me that P(X>_11) = 0.0532... which is bigger than 0.05
when x=12, it is below the critical value
6. I think the clue lies in the question: how many would need to be cured before the 5% significance level.
7. (Original post by ZJuwelH)
I think the clue lies in the question: how many would need to be cured before the 5% significance level.
ok.. i'm starting to get you
So lets say the question was "How many of the 20 people tested would need to be cured for the results to be significant at the 5% level?"

Then would it be 12?
8. yep ur both right that was a good question
9. Kind of proud of myself, I've not done a hypothesis test in my life and with S2 on Wednesday I've certainly got the ball rolling as far as "revision" is concerned

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Updated: June 22, 2004
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