Assignments and Exercises

There will be a few short assignments to stimulate discussion and to identify weak areas. We will discuss each during class.

Exercise 1

Consider the following letter to the editor, AP article, and original information contained in the Mortality and Morbidity Weekly report. What key mistakes did the letter-writer make in interpreting the AP story? Did the AP article accurately report the MMWR findings?

To the Editor: On Page 4A (Nation & World) on Aug. 22, we are told by health authorities in Atlanta that “measles cases in the U.S. are at the highest level in more than a decade, with nearly half of those involving children whose parents rejected vaccination, health officials reported,” and “worried doctors are troubled by the trend fueled by unfounded fears that vaccines may cause autism.”

After reading this, I am very concerned about these worried doctors, who are unable to figure out for themselves that if nearly half of these measles cases are unvaccinated children, the obvious conclusion is that more than half of them are children of parents who opted for vaccination of their children. Looks like the parents who rejected vaccinations made the right decision, for whatever reason, since obviously their children are somewhat (even if only slightly) healthier. This indicates that their immune systems are obviously (at least slightly) healthier.

I am very concerned that “these worried doctors,” who didn’t pick up on the obvious, are making health decisions for you, me and our loved ones.

J.S. Duke Joelton 37080

This editorial was written in response to the following story (Mike Stobbe, Aug 21, 2008)

ATLANTA — Measles cases in the U.S. are at the highest level in more than a decade, with nearly half of those involving children whose parents rejected vaccination, health officials reported Thursday.

Worried doctors are troubled by the trend fueled by unfounded fears that vaccines may cause autism. The number of cases is still small, just 131, but that's only for the first seven months of the year. There were only 42 cases for all of last year.

"We're seeing a lot more spread. That is concerning to us," said Dr. Jane Seward, of the Centers for Disease Control and Prevention.

Pediatricians are frustrated, saying they are having to spend more time convincing parents the shot is safe.

"This year, we certainly have had parents asking more questions," said Dr. Ari Brown, an Austin, Texas, physician who is a spokeswoman for the American Academy of Pediatrics.

The CDC's review found that a number of cases involved home-schooled children not required to get the vaccines. Others can avoid vaccination by seeking exemptions, such as for religious reasons.

Measles, best known for a red skin rash, is a potentially deadly, highly infectious virus that spreads through contact with a sneezing, coughing, infected person.

It is no longer endemic to the United States, but every year cases enter the country through foreign visitors or Americans returning from abroad. Measles epidemics have exploded in Israel, Switzerland and some other countries. But high U.S. childhood vaccination rates have prevented major outbreaks here.

with the AP article based on the Mortality and Morbidity Weekly Report

Exercise 2

Examine the following Figure taken from a submitted manuscript. Identify the mistakes and consider how you would correct each problem.

  • Figure for Exercise 2: Ratio of gene expression by age with n = 3 different animals in each age group. * p<0.05 different from 2-day old. fig1dyna.jpg

Exercise 3

Consider the following results of 5 trials of three drugs (A, B, and C) to lower cholesterol

Trial Drug # pts per group Diff in mean cholesterol Std dev of diff Std error of diff 95% CI for diff P-value
1 A 30 -30 191.7 49.5 [-129, 69] 0.55
2 A 1000 -30 223.6 10 [-49.6, -10.4] 0.002
3 B 40 -20 147.6 33 [-85, 45] 0.55
4 B 4000 -2 147.6 3.3 [-8.5, 4.5] 0.54
5 C 5000 -6 100.0 2 [-9.9, -2.1] 0.002

Questions

  • How would you (verbally) summarize the results of each trial? Which trial(s) show a significant treatment effect?
  • How would you design a figure to display the results in this table?
  • What assumptions are needed to make to make valid comparisons among the trials?
  • Compare the following trials
    • Trial 1 to Trial 2
    • Trial 3 to Trial 4
    • Trial 1 to Trial 3
    • Drug A trials to Drug B trials
    • Trial 2 to Trial 5
  • Which drug is best at reducing cholesterol?
  • Extra calculation questions: Verify each of the following quantities
    • Given the standard deviation and sample size, find the standard error
    • Given the standard error and sample size, find the standard deviation
    • Degrees of freedom
    • Given the mean difference and standard error, calculate the (a) 95% and (b) 99% confidence interval for the difference
    • Given the mean difference and standard error, calculate the (a) test-statistic and (b) P-value
Topic attachments
I Attachment Action Size Date Who Comment
fig1dyna.epseps fig1dyna.eps manage 28.5 K 20 Oct 2008 - 10:48 ChrisSlaughter Exercise 2 plot
fig1dyna.jpgjpg fig1dyna.jpg manage 34.5 K 20 Oct 2008 - 10:50 ChrisSlaughter Exercise 2 plot
Topic revision: r6 - 17 Dec 2008, ChrisSlaughter
 

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