Monday, April 21: Review of Confidence Interval.
comp screen (p 381): 23.2 21.2 28.9 27.7 29.1 27.3 16.1 22.6 25.6 34.2 23.9 26.8 20.5 34.3 21.4 32.6 26.2 34.1 31.5 24.6 23.0 28.6 24.4 28.1 41.3
known pop sd = 6
check for outliers
find the mean
build a reasonable confidence interval
We are _________ sure that the true mean of the data is between _________ and __________ .
Creating a null and alternate hypothesis.
example one (taken from http://www.unc.edu/~blopes/files/stat11spring03/Files/HypothesisTesting.pdf):
set null hypothesis
always equal to. always AGAINST what you want to prove.
set alternate hypothesis
one or two tail test?
set alpha level
what percent sure do we want to be that we are correct?
check data (if possible)
outliers with appropriate methods
check shape of data, etc.
bimodal is a big problem.
run analysis (get z-score, p-score)
compare and analyze
Tuesday, April 22:
0) 40 grocery receipts, SRS. National average in grocery spending is $150. We are looking at the amount spent at our local grocery store.
mean= $141
sd pop = $30.2
can we conclude that the amount spent at our local grocery store is different than that spent nationally?
1)
reading Gigi: comp screen (p 381): 23.2 21.2 28.9 27.7 29.1 27.3 16.1 22.6 25.6 34.2 23.9 26.8 20.5 34.3 21.4 32.6 26.2 34.1 31.5 24.6 23.0 28.6 24.4 28.1 41.3
known pop sd = 6
Times New Roman: 22
Question: is Gigi harder to read than Times New Roman?
2) Here are 6 measurements of the electrical conductivity of a liquid: 5.32, 4.88, 5.10, 4.73, 5.15, 4.75.
The liquid is supposed to have a conductivity of 5.
The measurements above are an SRS from the population. The population has sd of 0.2
Can we show the liquid does not have a conductivity of 5?
3) Sulfur compounds cause "off-odors" in wine, so winemakers want to know the odor threshold--the lowest amount of sulfur a human nose can detect. For DMS (dimethyl sulfide), trained wine testers can detect it at levels of about 25 micrograms per liter. We want to see if the threshold for untrained noses is less sensitive. Here are the odor thresholds for 10 untrained students:
31 31 43 36 23 34 32 30 20 24
sd = 7
Give a 95% confidence interval for odor threshold of the students
run a hypothesis test checking to see if students have a higher threshold than experts.
Wednesday, April 23:
Thursday, April 24:
Friday, April 25: