Epidemiological Research Trivia Quiz!

This clinical question is a prognosis question. It is asking about the potential outcome or risk of post-operative complications in teenage patients who are obese compared to those who have normal weight prior to open appendectomy. The question is seeking to understand the future course or prediction of outcomes for these patients.

The use of an appropriate comparison group is the key feature that distinguishes analytic from other types (descriptive) of studies.

The key difference between a cohort and case-control study is that, in a cohort study, subjects are enrolled on the basis of their exposure, whereas in a case-control study subjects are enrolled on the basis of whether they have the disease of interest or not. Both types of studies assess exposure(s) and disease status. While most cohort studies are conducted over several years, some, particularly those that are outbreak-related, are conducted in days.

Note that person-time at risk is not calculated in case-control, cross-sectional or ecological studies. It could be calculated in a RCT but the data in this table is unlikely to refer to one as we are not informed about how many persons were randomly allocated to treatment (or exposure) vs. control group (unexposed) we are just told how many of these have (developed) the disease or outcome of interest.

70/195,000=0.000359 (x100,000)=35.9 per 100,000 person-years

This clinical question falls under the category of Therapy. It is asking about the effectiveness of two different treatments (varenicline and nicotine replacement therapy) for long-term smoking cessation in male heavy smokers newly diagnosed with COPD. The question is focused on finding the best treatment option for this specific patient population.

Clearly, to answer a therapy question a randomised controlled trial is the best design to inform about treatment efficacy. In addition, to be able to avoid information bias, the trialists would have to think of a smart way to blind the patients to the treatment they would receive...

A cohort study is the best design for this type of PROGNOSIS question. A cohort study will give you the actual rate of post-operative complications in both the exposed (teenagers with obesity prior to surgery) and the unexposed (teenagers with normal weight prior to surgery) groups, enabling you to compare these (often done with the calculation of a relative risk)

The best way to answer this question is to first build a 2x2 table summarising the data (exposure status in rows, disease status in columns) provided in the text Cases Controls Total Exposed (a) 50 (b) 50 100 Not exposed (c) 50 (d) 150 200 Total 100 200 300

First, we needed to calculate the incidence rate (IR) among those who were not exposed:
30/225,000=0.000133 (x100,000)=13.3 per 100,000 person-years
(we have calculated the incidence rate among the exposed before = 35.9)
Now, to calculate the relative risk we simply divide the IR among the exposed by the IR among the unexposed: 35.9 person-years / 13.3 person-years = 2.70.

The contributions of these individuals were discussed on Lecture 10 (historical overview of key contributions to the discipline)

The population is teenage patients having surgery (note that surgery is not the study exposure – everyone in the study is having surgery). The study exposure is being obese prior to surgery, and the comparison group is all those with normal weight (unexposed). The outcome is complications following surgery