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Both the exposure and outcome are measured at one snapshot in time, so this is a cross-sectional study.

It is not a cohort study or a case-control study as there is no longitudinal aspect. Furthermore, in case-control designs, researchers select cases and controls based on the presence or absence of the outcome, respectively, and look back in time for exposures.

It is not an ecological study – in an ecological study, data are measured at the group-level, not the individual level.

It is not a randomized controlled trial, because we are not assigning people to be members of a gym. We are simply observing whether or not they are members of a gym, and whether or not they have depression.


Answer: c
This is selection bias. Individuals who visit a local park on a rainy day may differ systematically to the general population.


Answer: b
An odds ratio of less than the null value of 1.0 indicates that being a gym member might be a protective factor against depression (but note that the confidence interval spans the null value of 1).



odds ratio= null value of 1.0

risk ratio= null value of 0


Answer: e
The outbreak is lasting for longer with more of a plateau, which implies a contamination event that is lasting for some time


Answer: c ((35000*5)/126120000)*100000 or (35000/(126120000/5))*100000 or 35000/((126120000/5)/100000)


Answer: d
Risk ratio = (20/100) / (5/100) = 4
Odds ratio would be (20/80) / (5/95) == (20 * 95) / (5 * 80) = 4.75


Answer c

The effective reproduction number is the basic reproduction number R0 multiplied by the proportion of the population who are susceptible 8*(1- 0.25)=6


Answer: Contemplation

In the contemplation stage, people are intending to start the healthy behaviour in the foreseeable future. People recognise that their behaviour may be problematic, but may still feel ambivalent toward changing their behaviour.


Answer: Lack of social support from her housemate reflects lack of opportunity to change according to the COM-B model.

The COM-B model stands for Capability, Opportunity, Motivation and Behaviour.


Answer: c
Secondary prevention is about trying to detect a disease early and/or to stop if from getting worse, in the asymptomatic population


Answer: e
Overestimating survival duration for a disease because of a relative excess of cases detected which are slowly progressing, compared to those with a shorter preclinical phase (perhaps those that result in premature death) is an example of length time bias.


Answer: a
Here, the positive predictive value is 132/1,115 = 0.118, or 11.8%.

Interpretation: Among those who had a positive screening test, the probability of disease was 11.8%.


Answer: d
This describes the UK model