Mean = np = 15(0.9) = 13.5
g.
What is the standard deviation of the number of students who own a cell phone in simple
random samples of 15 students?
ඥ15(0.9)(1 − 0.9)
= 1.16

8.
For the following descriptions, list experimental units (or subjects), factors, levels,
treatments, and response variables.
1.
Veterinarians are interested in finding out which brands of dog food cause dogs to gain the
most weight.
Sixteen dogs younger than 5 and sixteen dogs older than 5 are selected and given
either Science Diet, Pedigree, Alpo, or Purina.
Factors:
age
brand
Levels: greater than 5, less than 5;
SD,
Pe,
A,
Pu
Treatments
> 5
SD,
> 5
Pe,
> 5
A,
> 5
Pu,
< 5
SD,
< 5
Pe,
< 5
A,
< 5
Pu
Response variable: weight
2.
A forester wants to know which of three types of tree (palm, pine, oak) does best resisting
hurricane force winds.
He selects 10 pieces of wood from each type of tree and subjects it to
hurricane force winds. He then records the level of damage for each type of wood on a scale
from 1 to 10.
Factors:
type of tree
Levels: palm, pine, oak
Treatments: palm, pine, oak
Response variable: level of damage on a scale of 1 to 10
3.
A corporate manager is interested in finding the best way to improve productivity. He wants
to see if reading a book or not or attending a seminar or not has the most impact on productivity.
He assigns the treatments to 8 branches of his company.
Factors:
book
seminar
Levels: read a book, didn’t read a book; attended seminar, didn’t attend seminar
Treatments:
book and seminar, book and no seminar,
no book seminar, no book and no seminar
Response Variable: productivity
SD
Pe
> 5
A
Pu
< 5
SD
Pe
A
Pu
pine
palm
oak
seminar
book
no seminar
seminar
no book
no seminar

4.
Doctors are interested in determining whether fitness level (low, average, high) and age
(20’s, 30’s, 40’s, 50’s) impact time to recovery after knee surgery.
40 people of various
ages and fitness levels are evaluated for time to recovery.
Factors:
fitness level
age
Levels:
low
average
high
20
30
40
50
treatments:
Lo20, Lo30, Lo40, Lo50, Av20, Av30, Av40, Av50, Hi20, Hi30, Hi40, Hi50
response variable: time to recovery
9.
Read the following descriptions, and tell what source of bias(es) each represents
(undercoverage, non-response, response bias, or poor wording of questions).
1.
A mail survey is conducted to determine what percentage of Americans are vegetarian or
vegan.
15% of households respond.
Non-response
2.
We would like to have an estimate of the percentage of people that participate in illegal drugs.
We call 3,500 households. In the study, no one says that they do illegal drugs.
Response bias
3.
How many Americans are supportive of welfare programs?
To find the answer, we will ask
“Given the failure of welfare in the US, do you feel welfare programs should be eliminated?”
poor wording in a question
How can this question be reworded so as not to cause bias?
Should the welfare program be continued or eliminated?

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- Spring '08
- Kyung
- Statistics, Normal Distribution, Probability, Standard Deviation