Antibiotic use in relation to the risk of breast cancer

| June 19, 2015

These questions refer to the paper by Velicer, C. M., et al. (2004). “Antibiotic use in relation to the risk of breast cancer.” Jama 291 (7): 827-35. (paper attached)

Question 1
a)    What was the aim of this study?  (1 mark)
b)    Provide one reason why a case-control design was suitable for this study.   (1 mark)
c)   Provide one limitation of using a case-control design in this study? (1 mark)

Question 2
a)    How were the cases defined?  (2 marks)
b)    Explain how the cases were selected      (2 marks)
c)    Explain how the controls were selected  (2 marks)
d)    Define the meaning of  “frequency matching” (2 marks)
e)    What is the purpose of “frequency matching”? (1 mark)
f)    Identify the reference population from which the study population was obtained (2 marks)
g)    Describe 2 potential selection biases that might be relevant to the selection of the study population from the reference population.  (2 marks)
h)    Discuss what consequences of these potential selection bias (from previous question) (2 marks)

Question 3
a)    Describe in detail how the main exposure of this study was measured? (2 marks)
b)    Identify 3 errors and/or biases that might have occurred during the measurement of exposure? (3 marks)
c)    List two actions the authors did to reduce error or bias in the measurement of exposure (2 marks)

Question 4
a)    State which potential confounders were collected. Explain how this information was collected (2 marks)
b)    Is “First-degree family history of breast cancer” a potential confounder? Explain your answer based on Table 1. (2 marks)
c)    Explain why age (at reference date) is not a potential confounder. Based your answer on Table 1 (2 marks)
d)    Summarise in a paragraph the main message of Table 1 (3 marks)

Question 5
In Table 3, the authors report that, compared with the reference category, the adjusted OR for  ? 1001 days of antibiotic use was ‘2.07 (1.48-2.89)’.
a)    Explain in your own words the meaning of the value 2.07(2 marks)
b)    Explain the meaning of (1.48-2.89) (3 marks)
c)    Is there any evidence of confounding here? Justify your answer. (3 marks)
d)    Is chance a possible explanation for this result? (2 marks)
e)    Calculate the crude OR between taking antibiotic >=1001 days, compared with 0 days. Show your workings. Use a 2×2 table (3 marks)

Question 6
a)    Is there evidence of a dose response relationship between number of days of antibiotic use and breast cancer? Why is this important (2 marks)
b)    Summarise in a paragraph the main message of Table 4 (3 marks)

Question 7
Suppose there was a mistake typing the days of antibiotic use for those who antibiotic for >=1001 days. Suppose that 15% of cases and controls from not exposed category were classified as exposed to >=1001 days.
a)    Re-compute the crude odds ratio between these two groups. Show your workings using a 2X2 table (3 marks)
b)    What type of bias is this? Explain what consequences produce this type of bias (2 marks)

Question 8
Suppose we discover that about 15% of the controls with 0 days of antibiotic use were labelled incorrectly as being exposed to >=1000 days.
a)    Re-compute the crude odds ratio between these two groups. Show your workings using a 2X2 table (2 marks)
b)    What type of bias is this? Explain why (2 marks)

Question 9
“We examined the sensitivity of the results to various assumptions about the ‘days of use’ antibiotic exposure variable in 8 separate subanalyses …” (page 830)
a)    Explain the purpose of performing these analyses (2 marks)
b)    Summarise the main findings from these sub-analyses (3 marks)

Question 10
a)    Explain in your own words the main conclusion from this study  (1 marks)
b)    Would you apply these conclusions of this study to the Australian population at risk of breast cancer? Why or why not? (2 marks)
c)    In a few sentences, summarise your general view on this study and its validity (3 marks) (Hint: base your answer on chance, bias and confounding)

Question 11
You are now planning to do a prospective cohort study to answer the same research aim.
a)    Describe your study population? (2 marks)
b)    Describe your comparison population (2 marks)
c)    Describe two the advantages of using this study design? (2 marks)
d)    Mention two disadvantages? (2 marks)


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