Analytic Approaches in Epidemiology (401175)

This assignment is based on the learning objectives and concepts as described in the Unit Learning Guide. There are a total of 75 marks and this assignment will contribute 50% towards the total assessment for this subject.

Your assignment should be typed, with adequate space left between questions. Assignments should be submitted via vUWS. Be as concise as possible in your answers, and note that there are specified space-limitations for each question.

Please note this is an individual exercise.
Late assignments will not be accepted without prior approval.

QUESTION 1: [25 marks]
A prospective cohort study of psychiatric outpatients with a history of suicidal ideation was conducted, investigating the effect of alcohol consumption and incidence of attempted suicide over a follow-up period of 24 months. The data at the end of the follow-up period for males and females are given below.

Males
Alcohol consumption Cases Participants
Light 5 250
Heavy 23 375

Females
Alcohol consumption Cases Participants
Light 25 250
Heavy 52 167

Assume no loss to follow-up and that all participants were followed over the follow-up period.

Discuss statistical interaction and confounding by sex for the following effect measures

-Risk difference
-Risk ratio
-Odds ratio

QUESTION 2 [10 marks]

Propose a causal diagram of the relationship between alcohol consumption and attempted suicide, based on the variables provided above. Provide a narrative description (1 paragraph only) of the causal diagram incorporating findings from your analysis in Question 1.

QUESTION 3 [10 marks]

Estimate the RR closest to the null value that would be required for a given confounder (C) (i.e. RRC|suicide) to account for the adjusted association between alcohol consumption and attempted suicide (i.e. RRalcohol|suicide) in Question 1.

QUESTION 4 [30 marks]

The data in the table below are taken from the National Mental Health Survey, a large, nationally representative cross-sectional prevalence survey estimating 12-month prevalence of a range of mental health, service use, and disability factors in addition to socio-demographic variables. Similar questions regarding alcohol consumption and suicidal behaviour were asked of participants. An extract of the data are given below, stratified by males and females.

Males
Alcohol consumption Cases Participants
Light 31 2885
Heavy 7 1109

Females
Alcohol consumption Cases Participants
Light 26 4387
Heavy 4 542

Discuss statistical interaction and confounding by sex for the following effect measures:

-Risk difference
-Risk ratio
-Odds ratio

In your discussion compare your estimates with those from Question 1. Comment on similarities or differences on effect estimates, and likely reasons for these similarities or differences (limit of 1 page).