Statistical Analysis: Determining Confidence Limits and Probability of Error

[sosme]

Can someone please help me figure out if my attempts are right? or if I am using the right method?


in one study on 20 men. the upper confidence limit of a 90% confidence interval is 62.3 grams, and the upper confidence limit of an 80% confidence interval is 54.8 grams. What would the lower confidence limit of a more appropriate 95% confidence limit be?

*I got a negative value for the lower confidence limit of -9.2 but it doesn't make sense. I solved for xbar by substituting the number I got from simga thru the CI formulaFind P(Mu > xbar); where xbar = -96.52, Mu0 = -34.21, n = 15, s2 = 32193.0551
**I wanted to use the t-distrbtion formula but I am not sure about Mu0, do I assume that Mu0=Mu and for s do I just plug it into this formula http://www.psych.utoronto.ca/courses/c1/chap7/chapte17.gif
but the thing is I see in my book s, sigmaxbar, sigma -> what's the difference between these, they seem like all the same


Calculate xbar where P(Mu > xbar) = 0.025, df = 20, Muxbar = 39.4, sigmaxbar = 28.7

*I tried to use the t-distriubution formula but I am still confused about the difference between xbar, Mu0, muxbar and Mu they seem like the same :S espiecally muxbar (is that the SD of the mean sample but then isn't that xbar :S Can I just plug sigmaxbar into S in the formula t = (xbar - mu)/(s/sqrt n) :S:SIn a similar test that was powered at 95%, you examined whether the use of advil among women attending your store was different from the general population. You conducted the test with 98% confidence, and found that the use of advil at your store was higher, but similar to and not significantly different than the general population. What was the probability that you were wrong?

Choices
a. 0.050
b. 0.020
c. 0.200
d. None of the other answers

*I thought that it was 0.02 at first but then I started thinking about the 95%, what does that mean? What about alpha error?Your friend is saying that you should not be using a Z or T test to test your hypothesis because the distribution of advil use in the general population of women is highly skewed. What do you say?
1) we will redo the tests in a way that does not rely on normality
2) It is fine because the Central Limit Theorem states that Sigmaxbar = Sigma0 / sqrt (N)

***I narrowed it down to these two but I can't figure out whether it's 1 or 2. How do I reason this out? I know that with CLT that statement is right but does that mean it's correct for this question?thank you so so much

 

[lippyka]

in advance!!For the first question, you are using the wrong formula. You should be using the normal distribution formula to calculate the lower confidence limit: Lower Confidence Limit = xbar - (1.645 * sigmaxbar/sqrt(n)) For the second question, the correct answer is 1). Since the population is highly skewed, a normal distribution will not accurately represent the data, so it would be better to use a different test that does not rely on normality.