Epidemiology

According to Cwikel (2006) Epidemiology is the science that investigates causes, patterns, and effects of health, and diseases within a given population. It is a governing body in public health, and it is usually used in policy making by governments. The paper illustrates the difference between experimental and observation epidemiology design. It will also discuss the conditions where a case-control study can be used as opposed to a cohort study.
Rosenbaum (2002) defines observational epidemiology design as one that draws inferences from the sample where the researcher does not control the independent variable. For example, the researcher might determine the possible effects of medications on the subjects, where the allocation of subjects to a treated unit versus a control component is beyond the researcher’s control. From the literature review, the researcher does not assign exposure status. Here, the research observes and measures the exposure status of the sample under investigation. In epidemiology, exposure is a situation where there is contact or close contiguity to a substance, pathogen, radioisotope, or more substance by absorbing, breathing, or exact contact on the eyes, or skin. Furthermore, exposure can be for a short time or for a long time chronic illness. 
There are three types of cases in Experimental epidemiology: randomized control trial frequently used for new medicine or drug testing. The field trial where the researcher conducts research on those that are at a high risk of conducting an illness, and finally, the community trial where the investigator conducts investigations research on social originating an illness (Aschengrau and Seage, 2007). From the literature, Experimental studies include people or communities within a given location. In that, exposure can be assigned to a person in clinical trials where new medicines are tested. Similarly, exposure could be assigned to a community, for instance, when educational campaigns are taken to institutions, cities or towns. Therefore, this design can be used to test whether a certain antibiotic is effective. 
When studying the frequency of an infectious disease like tuberculosis, the researcher can use both experimental and observational epidemiology. In experimental design, the investigator will test a hypothesis about the disease or treatment that can be used in a group of people. For instance, the effective a certain drug can be used against the causing organism. The infected individuals can be grouped into two so that one group receives the drug while the other gets a placebo. Here the antibiotic is the study variable. In case, those who receive the antibiotic cure, then the drug can be said to be effective. When using observational design, the researcher will study causes preventions and treatments for an outcome. He or she will mainly observe as the infected individual undergoes treatment.  
A cohort study is an example of an observational design where the investigator selects a sample group of people who are exposed and another group of individuals who are not exposed. He then compares the two groups for some time to analyse the rate at which the illness occurs within the population. On the other hand, Case-control design, the investigator groups the targeted population based on the outcome. Cases are individual who have the outcome while the controls are the individuals who do not have the outcome. Additionally, the previous exposure is usually determined for both controls and cases to determine if cases have specific exposure than the control group. Therefore, a case-control study can only occur when the population is grouped based on the outcome.

Conclusion
Epidemiological research designs are aimed at revealing unbiased exposures like alcohol, biological factors, stress, or different chemicals to death and mobility. Therefore, the unpremeditated relationship between exposures and outcome is an important feature in Epidemiological.