Applied Statistical Methods

HSRP 734

Summer 2008

Homework 1 (25 points total)

Due: 5/29/2008

General instructions: 1) you may discuss any and all portions of the assignment with other members of the class. However, the homework you turn in must be your own. 2) A final answer is not sufficient. Please show your work for full credit.

Question 1 (5 points total):

Detection of Hypertension

Consider the following observed data on a procedure to detect Hypertension:

Rated as Hypertensive / Rated as Not Hypertensive
Has Hypertension / 56 / 13
Does Not Have Hypertension / 6 / 48

Calculate the Sensitivity (2 points) and Specificity (2 points) of the procedure to detect Hypertension. Would you use this procedure and why (1 point)?

Question 2 (15points total):

Vitamin A Supplementation to Prevent Children’s Mortality in Nepal

A large scale study was performed in Nepal to ascertain the effect of vitamin A supplement for preventing mortality in children. A 2x2 table giving the frequencies of survival at 1 year by treatment group can be described by:

Study Arm / Outcome / Alive / Died / Total
Placebo / 13,457 / 254 / 13711
Vitamin A / 13,033 / 298 / 13331
Total / 26,490 / 552 / 27042

Use this data to investigate the relationship between vitamin A and child mortality and to compare different measures of association.

a)Calculate the cell, row and column percentages (4 points)

Study Arm / Outcome / Alive / Died / Total
Placebo / 13,457 / 254 / 13,711
Vitamin A / 13,033 / 298 / 13,331
Total / 26,490 / 552 / 27,042

b)For a child in the Vitamin A group, what are the odds of death (4 points)?

c)Give the odds of death for the Placebo group (2 points). What is the ratio of the odds of death for the Vitamin A group to Placebo (2 points)?

d)Estimate the relative risk of mortality for vitamin A vs. placebo (2 point each). Interpret the relative risk (1 point).

Question 3 (4 points total):

Write a sentence or two as if for the Lancet that reports the investigation of the relationship and their results between vitamin A and child mortality (2 points). Explain in a brief sentence or two why there is uncertainty in the estimated measure of association (2 points).

Question 4 (1 point):

When is the Odds Ratio of an exposure close to the estimate of Relative Risk? Give justification for your reasoning.

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