UCLA STAT XL 10
Introduction to Statistical Reasoning
Instructor: Ivo Dinov, Asst. Prof.
Departments of Statistics & Neurology
Wednesday, 7:00 PM, Apr. 17, 2002
Please, turn in your homework before class on the due date. See the
HW submission rules. On the front page include the
(HW_1_1) Consider the following studies:
Study 1: A researcher was interested in whether intelligence
level depends on body weight. 1000 people were selected from a group of
volunteers and divided in 4 groups. The first 250 were considered under-weight,
second group of 250 were
below average weight, another 250 over
the average and the last group of 250 over-weight. The subjects
underwent a comprehensive cognitive and psychological examination and scores
(integer the range 0 to 200) were assigned to all subjects.
Study 2: A technician is interested in the effects of using different
baking temperatures on the impact strength of particle board. 20 boards
are randomly allocated to 20 different baking temperatures. After the boards
are baked, they are sent to a laboratory where the impact strengths are
For each study, describe what treatment is being compared and what
is being measured to compare the treatments.
Which of the studies would be described as experiments and which
would be described as
For the studies that are observational, could an experiment have been carried
out instead? If not, briefly explain why not.
For the studies that are experiments, briefly discuss what forms of
blinding would be possible to be used.
In which of the studies has blocking been used? Briefly describe
was blocked and why it was blocked.
(HW_1_2) The following data represent the daily number of parking
tickets given out on UCLA campus over a period of 29 days.
42, 47, 46, 35, 43, 39, 38, 40, 50, 37, 68, 37, 47, 44, 49
41, 34, 38, 41, 36, 42, 38, 38, 58, 34, 32, 42, 49, 52.
By hand, construct a stem-and-leaf plot of the data using an appropriate
Calculate the five number summary for the data (min, lower quartile,
quartile and max). Note: If there are x indices
of numbers below the median then the (x+1)/2 -st number in the ordered
observations, see stem-and-leaf plot, gives you the value of the lower
quartile. The upper quartile is computed identically as the lower
quartile, except that you take the value of the observation half-way between
the median and the max-observation.
By hand, draw a box plot for this set of data. Show your work.
Using your plots, in plain English, briefly comment on the data and the
story the above summary/plots convey.
\Ivo D. Dinov, Ph.D., Departments of Statistics and Neurology,
UCLA School of Medicine/