Stat 250: Biostatistics
Homework Set #3 Solutions
Due Friday, January 30, 1998
Results of research studies are typically published in one of hundreds of scientific journals, such
as The New England Journal of Medicine and The Journal of the American Medical Association.
The authors of such journal articles invariably follow a standard scientific format, which
includes:
an INTRODUCTION section, which describes the scientific problem at hand, including
an overview of the current literature available on the topic
a MATERIALS AND METHODS section, which describes the scientific and statistical
procedures used in the research study
a RESULTS section, which describes the scientific and statistical results of the
research study
and a DISCUSSION section, which includes the authors' interpretation of the results,
and since research is a never-ending venture, describes what future research on the
topic might entail.
Recall that the results of research studies should only be extended to population(s) with similar
characteristics to the one(s) studied. As a result, authors summarize the characteristics of the
study subjects in detail in the Results section. For example, an author might describe the sample
of research subjects as follows: their average (or median) age, the number (or proportion) of
males and females, their range of weights, etc. The characteristics described depend on what is
particularly relevant to the topic at hand.
To complete this assignment, use Minitab to describe some of the data collected on this class in
the beginning of the semester. The data can be accessed in Minitab at:
I:\hammond\instruct\stat\250\spr98_001\formA.mtw
Specifically, use Minitab to describe the age, gender, and grade point averages of the students.
Also, pick one other variable of interest to you to describe. [Recall that categorical (binary) data
are typically described using proportions, while measurement (discrete or continuous) data are
described using ranges, medians, averages, and standard deviations.]
Once you have analyzed the data, write one paragraph, containing only 5 sentences as follows:
The first sentence should indicate the number of students included in your "study". The second
sentence should describe the gender of the students. The third sentence should describe the age
of the students. The fourth sentence should describe the grade point average (GPA) of the
students. And the fifth sentence should describe one other characteristic of the students based on
the other variable you chose. Submit your paragraph typed, double-spaced, on white, 8½ x 11
paper. Again, make sure you include your name and student ID number. This assignment is
worth 5 points (one point for each of your 5 sentences).
An example of a portion of a sample scientific article about chronic appendicitis is on the back of
this page. Read the article, and note how the author uses descriptive statistics (number of
patients, number of males and females, range of ages, average age, percent having normal
appendices, etc.) to describe the study subjects in the Results section.
There is obviously no one correct solution for this homework set. However, one possible
solution follows:
Ninety-two (92) students in the first section of Statistics 250 completed a 50-question
data collection form the week of 12 January 1998. The questionnaire asked students about their
family background, education, leisure activities, personal belongings, and residence and personal
life. Of the 92 students, 49 (53%) of the students were male, and 43 (47%) of the students were
female. The students ranged in age from 18 to 27 years, with a mean age of 20.5 years. The
grade point averages of the students in the study ranged from 2.02 to 3.98, with a mean grade
point average of 3.07. The majority of the students, 82 (89%), were Caucasian, 7 (8%) were of
Asian or Pacific Islander descent, 2 (2%) were African-American, and 1 (1%) was of another,
unspecified racial background.
This above paragraph is derived from the following Minitab output:
q1
1
2
N=
Count Percent
49
53.26
43
46.74
92
Variable
q3
q20
N
92
92
Mean
20.478
3.0698
Median
20.000
3.1200
Tr Mean
20.329
3.0766
Variable
q3
q20
Min
18.000
2.0200
Max
27.000
3.9800
Q1
20.000
2.6725
Q3
21.000
3.4675
q4
2
3
4
5
N=
StDev
1.371
0.4851
SE Mean
0.143
0.0506
Count Percent
7
7.61
2
2.17
82
89.13
1
1.09
92
COMMENTS:
1. It is incorrect to refer to the sample of students as the “sample population.” Either “sample”
or “study population” is correct, but not “sample population.”
2. Rather than starting a sentence with a number like “49 of the students were male,” spell the
number and then put the number in parentheses, like “Forty-nine (49) of the students were
male.”
3. It is best to give numbers and percentages, like “49 (53%) of the students were male, and 43
(47%) of the students were female.”
4. Do not make the reader assume anything when you report the results of an analysis. Just
because there are 92 students and 49 males, it does not necessarily imply that there are 43
females. Some of the respondents may have left gender blank, and some of those
respondents could have been male. So, report the number in each category.
5. Don’t report numbers to an excessive number of decimal places. “The average age is 20.5
years” is sufficient. “The average age is 20.478 years” is excessive.