# Biostatistics Class (HSD269-XH81),Fall 2014

August 30, 2017

Question
I. Table 1 lists all students in the biostatistics class (HSD269-XH81),Fall 2014.

Table1

1.Select a simple random sample of size 5 from HSD269-XH81 population by entering

The table of random digits (Table A) in row 24. What is a simple random sample?

2.Suppose that the biostatistics instructor would like to know whether noticing students

two days prior to a quiz would ameliorate their score on the quiz. The instructor thus

decides to create two groups of students at random. One, the treatment group composed

of8 students, will be noticed one week prior to taking the quiz; the other, the control

group of 13 students, won’t receive any notice. The process of randomly assigning

groupsto conditions is called randomassignment.

1 Aloi Deheza, Maria Virginia

2 Blake, Sevon C

3 Brown, Unique

4 Campos, Juandy Y

6 Echebiri, Raphael I

7 Flores, Brandon C

8 Galan Reinoso, Isabel M

9 In, Sophanary

10 Leonidas, Rilloux

11 Maria, Keila E

12 Merricks, Chevalin

14 Ogbaloi, Sandra E

15 Paulino, Sheena

16 Peluso, Amanda

17 Polanco, Melissa C

18 Rodriguez, Carolina

19 Rodriguez,Jazmine G

20 Santiago, Vanessa

21 Viloria, Kalela C

22 Williams, Iyisha

1.Select a simple random sample of size 5 from HSD269-XH81 population by entering

thetable of random digits (Table A) in row 24. What is a simple random sample?

2.Suppose that the biostatistics instructor would like to know whethernoticing students

two daysprior to a quiz would ameliorate theirscoreon the quiz. The instructor thus

decidesto create two groups of students at random. One, the treatment group composed of8 students, will be noticed one week prior to taking the quiz; the other, thecontrol group of 13 students, won’t receive any notice. The process of randomlyassigning groups to conditions is called randomassignment.

b)Is random assignment the same as simple random sampling? Explain your

c)Identify the explanatory variable and response variable in this study.

d)Is this an experimental or observational study? Why?

e)What is a confounding? Cite three possible confounding variables in this study

f)Why experimental studies are called the “gold standard” of research?

g)An experimental design is different from both cohort study and case-control

study(two observational studies), what is the main mechanism that differentiates

experimentalstudies from observational studies?

h)Use Table A starting in row 12 to select your treatment group andcontrol

group.List the students’ name of each group.

II.Medical test. A scientist designed a medical test for a certain disease.Among 100

patientswho have the disease, the test will show the presence of the disease in 97cases

outof 100, and will fail to show the presence of the disease in the remaining 3cases out

of100. Among those who do not have the disease, the test will erroneously showthe

presenceof the disease in 4 cases out of 100, and will show there is no disease in the

remaining96 cases out of 100.

(a)What is the probability that a patient who tested positive on this testactually has

thedisease, if it is estimated that 20% of the population has the disease?

(b)What is the probability that a patient who tested positive on this testactually has

thedisease, if it is estimated that 4% of the population has the disease?

III. A group of 2000 randomly selectedadults were asked if they are in favor of or against cloning. The followingtable gives the responses.

a) If one person is selected at random from these 2000 adults,find the probability

that this person is:

i. in favor of cloning

ii. against cloning

iii. in favor of cloning given the person is a female

iv. a male given the person is against

b) Are the events “male” and “in favor” mutually exclusive? Whatabout the events

“in favor” and “against”? Why or why not?

c) c) Are the events “female” and “no opinion”independent? Why or why not?

IV. Assigning Grades.Professor CJ uses a normal distribution toassign grades in his

Biostatistics class. He assigns an A to students scoring more than2 standard deviations

above the mean and an F to students scoring more than two standarddeviations below the

mean. He assigns a B to students who score between 1 and 2standard deviations above

the mean and a D to students who score 1 and 2 standard deviationsbelow the mean. All

other students get a C. what percent of the class receives eachgrade assuming the scores

are normally distributed?

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