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ST 732, DATA ANALYSIS PROJECT, SPRING 2007
Due Thursday, April 26, 2007
N.B.: This is a “closed” take-home project. Thus, you may not collaborate with or discuss the
assignment with any other person (whether in the class or not), nor may you consult with anyone
except the instructor for help or clarification (not even your mother). You may use the class notes,
books, or any other reading material you like.
Because you are taking a course in longitudinal data analysis, you have been approached by a
group of medical researchers to serve as a statistical consultant. The researchers have conducted a
clinical trial to investigate the effects of two oral treatments for toenail dermatophyte onychomy-
cosis, a common infection of the toenail. Here is some background.
Onychomycosis, known popularly as toenail fungus, is a fairly common condition that not only
can disfigure and sometimes destroy the nail but that also can lead to social and self-image issues
for sufferers. It has been estimated that between 2% and 18% of of people world-wide and up to
5% of people in the United States are afflicted by some form of onychomycosis. The likelihood of
affliction is rare among children under 18 but increases with age, and it is estimated that up to
48% of people have had at least one episode by the age of 70. The big toe and little toe are the
most likely to be afflicted. Tight-fitting shoes or hosiery, the sharing of common facilities such as
showers and locker rooms, and toenail polish are all thought to be implicated in the development
of onychomycosis.
Onychomycosis is distinguished by discoloration of the toenail, which itself becomes thick,
overgrown, and crusted with debris. This condition is often accompanied by a foul-smelling odor
caused by accumulation of debris under the nails. In various versions of the disease, the nail may
crumble and gradually fall off, become so thick that wearing shoes causes extreme discomfort, or
develop a soft, powdery surface.
Onychomycosis can be caused by several types of fungi known as dermatophytes, as well as by
nondermatophytic yeasts or molds. The study conducted by the researchers involved sufferers of
the particular type caused by dermatophytes.
The standard approach to treatment of toenail dermatophyte onychomycosis involves removal
of as much of the afflicted part of the nail as possible, followed by application of a topical antifungal
ointment or by a course of treatment with an oral antifungal medication, for which better outcomes
are generally obtained than with ointments. The study conducted by the researchers was focused
on comparison of two oral medications, terbinafine (given as 250 mg/day, denoted as treatment 1
below) and itraconazole (given as 200 mg/day, denoted as treatment 2 below).
The trial was conducted as follows. 200 sufferers of advanced toenail dermatophyte onychomy-
cosis in the big toe were recruited, and each saw a physician, who removed the afflicted nail as
described above. Each subject was then randomly assigned to treatment with either terbinafine
(treatment 1) or itraconazole (treatment 2). Immediately prior to beginning treatment, the length
of the unafflicted part of the toenail (which was hence not removed) was recorded (in millimeters).
Then at 1 month, 2 months, 3 months, 6 months, and 12 months, each subject returned, and the
length of the unafflicted part of the nail was measured again. Intuitively, as the nail grows out
(hopefully without signs of onychomycosis, due to the effects of treatment), this length is likely to
increase if the treatments are working, with the better treatment resulting in longer unafflicted nail
lengths on average.
Also recorded on each subject was gender and an indictor of the frequency with which the
subject visited a gym or health club (and hence might use shared locker rooms and/or showers).
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