University of Minnesota, Twin Cities
School of Statistics
Stat 3011
Rweb
Textbook (Wild and Seber)
Stat 3011 (Geyer) First Midterm (Computer Lab Part)
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General Instructions
The exam is open book, open web pages. You may use the computer,
a calculator, or pencil and paper to get answers, but it is expected
that you will use the computer. Show all your work:
- For simple computer commands, you may just write the command
you used and the result it gave on this test form.
- For complicated commands or plots, make a printout and attach
the printout to the test form (we'll provide a stapler).
No credit for numbers with no indication of where
they came from!
Suppose a random variable X has a normal distribution with
mean 25 and standard deviation 10.
- Find the probability that X is less than zero.
- Find the probability that X is between 25 and 30.
- Find the the 0.90 quantile of the distribution of X.
You may use the form below to answer this question.
A standard test for diabetes is based on glucose levels in the blood after
fasting (not eating) for twelve hours. For healthy people the fasting blood
glucose level has a normal distribution with mean 5.31 mmol/L
(millimoles per liter)
and standard deviation 0.58 mmol/L. For untreated diabetics the distribution
of fasting blood glucose level is also normal but the mean is
11.74 mmol/L and the standard deviation is 3.50 mmol/L.
- Find the probability that a healthy person has a fasting blood glucose
above 6.5 mmol/L.
- Find the probability that a healthy person has a fasting blood glucose
below 6.5 mmol/L.
- Find the probability that an untreated diabetic has a fasting blood glucose
above 6.5 mmol/L.
- Find the probability that an untreated diabetic has a fasting blood glucose
below 6.5 mmol/L.
You may use the form below to answer this question.
The file sally.txt contains a single variable
named sally for which measurements on 300 individuals are recorded.
- Draw some sort of plot that shows you the shape of the distribution
of the data.
(Hand in this plot. Be sure to put your name on the plot
before sending it to the printer. Either put your name in quotes as one
command or add the optional argument
main="your name here" to any
plot command.)
- Describe the shape of the distribution. Is it symmetric or skewed?
If skewed, which way? Is it unimodal or multimodal? Are there any outliers?
- Find the mean.
- Find the median.
- Find the standard deviation.
- Find the interquartile range.
- If you had to pick one measure of center and one measure of spread from
the four numbers just calculated, which would you pick? Explain. Make it
clear which is the measure of center and which is the measure of spread.
The form below automatically loads this data set
sally.txt (like the lecture section
examples). You don't need to anything to load the data.