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DS 1000

Assignment 3

2022

Question 1 (24 pts)

A study was conducted on horses to identify factors that might contribute to the formation of enteroliths —stones that form in the colon of the horse and eventually lead to blockage and    death. The given table summarizes disease status by sex: gelding, mare, and stallion.

Has Enteroliths?

Yes

No

Total

Gelding

29

41

70

Mare

28

32

60

Stallion

5

2

7

Total

62

75

137

a)   (3 pts) Calculate the marginal distribution for sex and the marginal distribution for disease status.

b)   (3 pts) Calculate the conditional distributions of sex given disease status.

c)    (3 pts) Calculate the conditional distributions of disease status given sex .

d)   (6 pts) Plot by hand the conditional distribution of disease status given sex .

e)   (3 pts) What can you say about the relationship between disease status and sex from your answer in d?

f)    (3 pts) Calculate the relative risk of enteroliths for mares versus stallions . Interpret.

g)   (3 pts) Calculate the odds ratio of enteroliths for mares versus stallions . Interpret.

Question 2 (8 pts)

Veterinarians often use nonsteroidal anti-inflammatory drugs (NSAIDs) to treat lameness in      horses. A group of veterinary researchers wanted to find out how widespread the practice is in the United States. They obtained a list of all veterinarians treating large animals, including         horses. They sent questionnaires to all the veterinarians on the list. Such a survey is called a     census. The response rate was 40%.

a)   (4 pts) What is the population for this survey?

b)   (4 pts) What is the sample?

Question 3 (12 pts)

What type of sampling technique was used in each of the following scenarios :

a)   (3 pts) Researchers waited outside a bar of interest. They stopped every 10th  person       who came out of the bar and asked whether he or she thought drinking and driving was a serious problem.

b)   (3 pts) Hoping to learn what issues may resonate with voters in the coming election, the campaign director for a mayoral candidate selects one block from each of the city’s         election districts. Staff members go there and interview all the residents they can find.

c)    (3 pts) A company packaging snack food maintains quality control by randomly selecting

10 cases from each day’s production and weighing the bags . Then they open one bag from each case and inspect the contents .

d)   (3 pts) Provincial police set up roadblocks to estimate the percentage of trucks with up- to-date registration, insurance, and safety inspection stickers.

Question 4 :(20 pts)

All pharmacists in the Canadian province of Ontario are required to be members of the Ontario College of Pharmacists. At the end of 2018, here are the types of practices that they had.

Practice Type

Number of Pharmacists

Community Pharmacy

11,323

Hospital or other health care facility

2,664

Academia or government

333

Industry

500

Corporate office, professional practice or clinic

167

Suppose the college is interested in obtaining members’ views and understanding of the 2012   Expanded Scope of Practice Regulations, which authorizes pharmacists to provide additional      services, including prescribing drug products for smoking cessation and administering the           publicly funded influenza vaccine. To be sure that the opinions of all practice types are                 represented, you choose a stratified random sample of 10 pharmacists from each practice type. Explain how you will assign labels within each practice type and then give the label numbers for the 50 pharmacists you selected.

Question 5 (20 pts)

Foresters were interested in studying a remote-sensing measure of standing timber as an          alternative to taking measurements on the ground. The study area was a 1200-acre pine forest in Louisiana on which the U.S. Forest Service first created a grid of 1410 equally spaced circular plots of 0.05 acre in size over a map of the forest. The ground survey then visited every 10th  plot and took measurements of tree volume.

a)   (10 pts) Assuming that the plots are numbered from 1 to 1410, explain how you would select a systematic sample of every 10th  plot.

b)   (10 pts) :Now choose a systematic random sample of 141 plots for the ground survey using Python.

Question 6 (16 pts)

Do people who write by hand have a better memory of what they write than those who write  using a keyboard? To test this, researchers had 36 participants in a study write down a long list of words read out loud to them. They were then asked to put aside their list and try to recall as many of the words as possible. Two methods of writing down words were used. One was using a blue-ink regular ball point pen and a notepad. The other was using a laptop equipped with a  full-size keyboard. The number of words correctly recalled was the response.

a)   (8 pts) Outline a completely randomized design to learn the effect of method of writing words on number of words correctly recalled.

b)   (8 pts) Describe in detail the design of a matched pairs experiment, using the same 36 subjects, in which each subject serves his or her own control.