L1: Classical Epidemiology

Question 1

What are the differences between clinical and community-based investigations?

Answer 1

Clinical Investigations:
Focuses on only sick people and results relate only to an individual in question. Such investigations aim at therapeutic use.

Community based: Here you look at both sick and healthy people, and the results relate to the population under study. Such investigations aim at therapeutic and preventive use and the results can be used in planning and evaluation public health decisions.

Question 2

What is the most important thing when designing a epi. study?

Answer 2

The reason behind the study, the study question. In communicable diseases a question could be “what is causing this disease and how does it transmit?”. You can also ask questions for non communicable diseases such as “do anti-smoking campaigns work?” or questions related to health services research such as “does patient satisfaction differ between private and public hospitals?”.

Question 3

Step by step epidemiology

Answer 3

1. Descriptive Epidemiology: understand the problem, identify cases and describe transmission, distribution etc.
2. Analytical epi. Establish cause of disease/determinants, define risk factors
3. Interventional Epi: change the situation.

1 and 2 = observational Epi.

Question 4

How do you accurately count disease cases?

Answer 4

The rate = #cases/population at risk

Prevalence = #cases at timepoint x/pop. at risk

Incidence = New cases in period x-y/pop. at risk

Question 5

What types of studies can you run?

Answer 5

1. Descriptive Studies: 1 group
   * Cross sectional studies
   * Longitudinal studies
2. Analytical studies: 2 or more groups
   * Cohort studies
   * Case-control studies
3. Intervention studies: 2 or more groups
   * Randomized controlled trials

1. Generate hypothesis
2. Test hypothesis
3. Test if intervention works

Question 6

Explain:

Cross sectional studies

Answer 6

In cross-sectional studies you sample and examine the pop. at risk at ONE TIMEPOINT. This allows to measure the prevalence rate.

Question 7

Explain:

Longitudinal Studies

Answer 7

A group/cohort of people is followed OVER TIME and new disease episodes are registered.

Not all individuals need to be monitored all the time, phased entry. Closed and open cohorts exist. Closed: all individuals are chosen before study begins. Open: newborns come into the study when they are born. You just set the number before the study.

Question 8

Explain what risk factors and confounding factors are and why bias and confounding can occur.

Answer 8

Risk factors are factors that are associated with the disease of interest. They cause an increase/decreased risk of getting this disease. In a study, you want to focus on the risk factor you choose, e.g. smoking -> lung cancer. But many other factors are associated with lung cancer, e.g. genetics, age etc. If you do not control for these so called confounding factors you risk bias and confounding in your study.

Question 9

How do cohort studies work?

Answer 9

Cohort studies compare a group exposed to a risk factor to one group that is not exposed; both groups are disease free. Cohort studies are observational and prospective, they measure the occurence of the disease over time.

You can study more than just one outcome, but only one exposure.
Cohort studies tend to be large-> expensive and difficult to runa nd analyze. Lets you calculate incidence and (relative) risk.

Question 10

What are case-control studies?

Answer 10

In case-control studies you choose a group that has the disease (cases) and one without (controls). Then you retrospectively investigate their exposure. This can establish how tighlty the exposure and outcome are linked.

Well suited for rare diseases and/or have long duration.
Allows to study only one outcome but several exposures. Tend to be smaller-> cheap and easy.