Lab 9 / Tutorial 1: Confidence intervals
The max grade for this lab is 110 but the scale is still 100 points. The 10 points are extra
credit.
The following video might be helpful:
Confidence interval
Note:
numbers are truncated. There is no need to use any data to perform actual test. The actual
P
-value is given to you.
Set-up
: The manufacturer introduced a new version of a machine and it was sued for not
disclosing the additional maintenance cost. The average annual maintenance cost for the older
model was $1170. Given the data for the recent machines, decide if the law suit holds water.
(Need to manually input the data into Excel).
What test/procedure should be run?
(Click for answer)
We need to compute the confidence interval (with 95% confidence)
What is the margin of error?
(Click for answer)
We need to compute standard deviation: type = StDev(Array1) and the answer is 1097.1. After that type
= Confidence.T(0.05,1097.1,12), where 12 stands for 12 data points. The answer should be 697.0661
What is the Statistical interpretation?
(Click for answer)

Theory tells us that the 95% confidence interval is equal to
[Average – Margin of Error,
Average + margin of Error].
In our case the average is equal to 1632.833, thus the interval is
[935.7673, 2329.899].
What is the conclusion?
(Click for answer)

Lab 9 / Task 1
In what follows use any of the following tests/procedures: Regression, confidence intervals, one-
sided t-test, or two-sided t-test. All the procedures should be done with 5% P-value or 95%
confidence interval.
Open
Brain
data. SETUP: It is believed that the larger the head circumference the larger the
brain volume should be. Given the data your job is to confirm or disprove this assertion.
1. What test/procedure did you perform?
Correct Answer

d. Confidence interval