Descriptive and Analytical Study Designs

In this unit, you learned that the association between variables (exposures) and outcomes can be investigated through descriptive or analytical study designs. The main types of analytical epidemiologic studies include the following:

Type of Study

Description of Study Type


Passively observe causes, preventions, and treatments for disease without interfering with its natural course.

Case Control

Involves the identification of cases- those with a disease- and controls – those selected with similar attributes (age, geography and engaging in similar activities) who do not have the disease. The characteristics of exposure for both groups are compared to determine the cause of disease. Finding controls to match the cases can be difficult and time consuming.


Prospective Cohort –a defined population which is observed over time for a specific exposure(s) to identify new cases of disease. This type of cohort study can be expensive if the observations are made over a long period of time.
Retrospective – uses data collected from surveys, interviews and records to determine exposure levels to a contagion. This method can be used in outbreak investigations in lieu of case control studies and the expense is much less than a prospective cohort study.
Historical Prospective – uses historical information already collected on a defined population and is used to conduct the study.


The observed study subjects are units of populations such as geographic areas (counties, states, countries, …)

Intervention (Experimental)

Involves the deliberate change of the study subject’s status. The introduced change can be in the form of medication, interventions or preventions.

Randomized Control Trial

Study participants are randomly assigned to groups to receive or not receive medical or other intervention or prevention.


A type of research in which the intervention is changed or introduced to a group that is not divided into exposure or non-exposure groups resulting in random exposure. This method of study is normally used in communities, schools and geographic areas.

Imagine you are an Epidemiologist at local department of public health. You received a call from Dr. Wilson, the Medical Director for a local nursing home facility, who reported 60 elderly residents exhibiting symptoms of vomiting and diarrhea. She was worried the residents were exposed to a stomach virus or have food poisoning.

Dr. Wilson provided you with the laboratory test results and asked you to perform an epidemiology investigation to determine the source of their illness.

  1. What type of study would you use and why? Your hypothesis is the residents became ill from a meal served within the past 48 hours. The suspected meal included grilled chicken, potato salad, biscuits, cake and ice tea. You are not 100% sure which item caused the illness but with consideration of the laboratory result you suspect the chicken caused the illness.
  2. What is the attack rate of those who eat chicken?
  3. Using the information in the data below, calculate the proper measure of association (odds ratio or relative risk) for the chicken using a Fourfold table (also called a 2 X 2 table). Your table should look similar to the example below.BIO250-U3-Assignment-FourFoldTable.PNG
  4. Do you have enough information to claim the chicken is the cause of the residents’ illness? Why or why not?
    Number of residents who eat chicken and were sick 35
    Number of residents who eat chicken and were not sick 15
    Number of residents who did not eat chicken and were sick 5
    Number of residents who did not eat chicken and were not sick 5

You may create your answers to the questions above, your fourfold table and your calculations in either a Microsoft Word or Excel document. Upload your file using the direction below.

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