+1 862 207 3288 This assignment has 4 questions and it will be marked out of 35. It is worth 35% of the total marks for Biostatistics B. It covers the material in modules S7, S8 and S9. It is assumed that you have a clear understanding of the content of these modules.
Question 1
In a study of intra-observer variability in the assessment of cervical smears, 3341 slides were screened for the presence or absence of abnormal squamous cells. Each slide was screened by a particular observer and then re-screened six months later by the same observer. The results of this study are shown in Table 1.1 below.
Table 1.1: Cross tabulation of the results of the first and second screening
Second screening
Present Absent
First
screening Present 1764 498
Absent 412 667
a) Do these data support the null hypothesis that there is no association between time of screening and diagnosis? Briefly explain by carrying out an appropriate test.
Question 2
A nested case-control study was conducted in the Hunter Region of NSW to examine whether patients who were current smokers of cigarettes had more complications after surgery than patients who were non-smokers. Tables 2.1 and 2.2 show the smoking status for cases (those with complications at the 6 week follow-up visit) and controls (those with no complications), separately by hospital.
Table 2.1: Count of the number of complications among smokers and non-smokers at Hospital 1
Hospital 1 Complication
Present Absent
Smoking status Smoker 42 22
Non-smoker 85 62
Table 2.2: Count of the number of complications among smokers and non-smokers at Hospital 2
Hospital 2 Complication
Present Absent
Smoking status Smoker 254 348
Non-smoker 96 172
a) Estimate the odds of being a smoker among patients who had a complication at 6 weeks and who had their surgery performed at Hospital 1.
[1 mark]
b) Estimate the odds of being a smoker among patients who DID NOT have a complication at 6 weeks and who had their surgery performed at Hospital 1.
[1 mark]
c) Calculate the odds ratio (and 95% confidence interval using Woolf’s formula) for having a complication among smokers compared to non-smokers based on the data from Hospital 1. [Hint: Do not use the formula in Module 7 because it’s not correct]
d) Verify your results in part c) using appropriate Stata commands
e) Conduct a test of homogeneity to determine whether it is appropriate to combine the information in Tables 2.1 and 2.1 using the Mantel-Haenszel method and comment on the results of the test.
f) Use Stata and the Mantel-Haenszel method to estimate the odds or complications among smokers relative to the odds of complications among non-smokers after adjusting for the potential confounding effects of hospital. Present the result and the 95% confidence interval.
g) Was hospital a confounder to the association between smoking and complications? Justify your answer.
h) Using the data provided above would it be appropriate to estimate the relative risk of complications associated with being a current smoker? Justify your answer.
i) Repeat part f but using logistic regression.
