Generally, logistic regression
Marking criteria
Marks are shown for each question.
Answers to each question must include the syntax used and the results from that syntax. The latter must include
those items, e.g. tables, graphs, and written text, and only those items,which are appropriate to answer the
questions. Assignment answers must be concise and well-presented, up to the standard of a presentation for
publication.
Do not include irrelevant computer output, do ensure that appropriate information only is presented and in a
logical sequence, and avoid use of excessive decimal places. Text must be clearly expressed and free from
grammatical errors. Word lengths must be complied with. A ‘brief paragraph’ has a limit of 50 words and is text
only. A ‘brief report’ has a limit of 300 words, but may include one summary table and/or one figure, only where
relevant.Note that paragraphs and reports must be self-contained, i.e. the main numerical findings must be
presented and quantified in standard ways – follow examples given in course notes.
Marks will be deducted if these criteria are not complied with.
1. Based on findings relating foetal exposure to tobacco in pregnancy and subsequent behaviour problems
arising in early childhood, and biologically plausible explanations for this association being causal (Williams et
al 1998), it is suggested that smoking in pregnancy may lead to later behavioural and developmental problems.
Use your individual dataset to examine the hypothesis that smoking in pregnancy is associated with later
educational attainment of the child (at age 14), using
(a) descriptive statistics;
(b) the appropriate test of association; and
(c) a logistic regression model, with appropriate output.
Write a brief paragraph stating your conclusions.
[6 marks]
2. Examine the relationship identified in 1 for confounding by the following socio-demographic factors (one by
one):
a. The sex of the child
b. Family incomeduring pregnancy
c. Mother’s education
For each of a, b and c separately, write a brief paragraph identifying whether confounding occurred, the direction
and extent of confounding, and explaining why this occurred.
[6 marks]
3. Add the variables in 2 to the logistic regression model in 1, and write a brief paragraph summarising
results, including all essential information and justification, and commenting on the direction and extent of any
confounding identified.
[3 marks]
4. Examine the association between educational attainmentand aggressive behaviour at age 14 years. Write a
brief paragraphsummarising results of this analysis.
[3 marks]
5. Re-do the analysis in question 3, adding the aggression variable to the model.Write a brief paragraph
summarising results, and commenting on the appropriateness of including aggressive behaviour in the model, any
differences to your model and why these changes (from the model in question 3) occurred, or if there was little
change, why this occurred.
[3 marks]
6. A plausible hypothesis is that higher maternal education might offset any adverse effect of maternal
smoking in pregnancy on educational attainment. Prepare an appropriate table (not using logistic regression) to
examine this hypothesis, combining the first two categories of maternal education.
[3 marks]
7. Fit a regression model which addresses question 6, construct an appropriate table of results, and write a
brief paragraph describing the results of the analyses in questions 6 and 7. Ignore other variables for this
analysis.
[5 marks]
8. What further analyses would you do to try to strengthen the argument for a causal effect between smoking in
pregnancy specifically and educational attainment of the child? Discuss particularly the issues around over-
controlling versus adjusting for confounding (brief paragraph). Do not do any further analysis.
[4 marks]