Health sciences and medicine biostatistics

Health sciences and medicine biostatistics

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 – 15 marks

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.

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.

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.