Modern-day epidemiology can be traced to the studies of William Farr and John Snow in their 19th century study into thecholera outbreak. These studies are essential in solving the transmission of disease as John Snow, the originator of epidemiology, did with cholera. He used analogical studies and his findings were fruitful in containing the disease which had killed many people, mostly workers whom he observed were working in congested conditions (Morabia, 2001).   

The study designs that are mostly used in epidemiology are quantitative and qualitative which are basically observational. Unlike these observational studies, clinical study design is experimental as it uses case studies and cross-sectional studies. It borrows from the results of the qualitative or quantitative studies in order to try out some types of medicine to identify which one could provide cure within a population, its patterns as well as the factors associated with it and the possible preventive measures. (Trochim, 2006).  The study designs basically deal with the systematic collection of observations concerning an epidemic. Statistics is the main method of collecting data in both qualitative and quantitative studies. These study designs are used by medical practitioners in order to conduct a thorough study into an epidemic and to translate the hypothesis, which is conceptual in this case, into one that is operational through clinical studies. The epidemiologist largely relies on primary data in carrying the study. Secondary data is also helpful, although it is mostly used in clinical studies. The Indians who gave the sailors cedar powder to cure scurvy relied both on primary and secondary data to administer cure in a process of clinical study, as well as those who tried lemon juice (Anderson, 2000). Qualitative study is done through observation and it is objective as opposed to quantitative which is subjective. Both studies may be carried out either by a paramedic or a non-paramedic. Through qualitative and quantitative studies, a theory is generated concerning the epidemic. Clinical studies involve trials and must involve paramedics strictly. It is largely subjective and relies more on informants rather than sample size. Qualitative study is predictive and it carries out surveys and data which are based on the sample size. It is objective in nature.

The aim of observational methods of epidemiological studies is to establish the causes as well as effects of a certain disease which is more widespread than usual. They are statistical in nature and they mostly give figures of the people affected by the epidemic as well as the casualties so that a suitable cure can be found through clinical studies. The aim is to address the cause as well as the effects of that particular epidemic. Quantitative study entails observing the participants of a selected population to determine the extend to which a certain disease has spread (Eyler, 2001). The participants are interviewed and surveys are made before an analysis is made. For qualitative study, the affected population is observed so that the people carrying out the study can gain an insight into understanding the patterns of the disease and determine what can be done to prevent further spread and the means of treating it if cure can be found. In cases of HIV/Aids, Qualitative studies are mainly interested in establishing how the pandemic has spread and the ways in which the population can be sensitized to arrest the spread. Statistics help in determining the extend of a disease, the patterns and ways of containing it.

During the early days of the ancient sailors beginning wit Christopher Columbus, the two observational designs of study were the mostly used. Sailors were dying at a high rate from scurvy and something had to be done. They tried clinical study using several possible foods and eventually lemon juice was tried and found to be effective in treating the disease. Sir Richard Hawkins is credited for the breakthrough during his voyage of the pacific in 1593 and he eventually recommended sour oranges and lemons to treat scurvy. Cure had been found but ignorance led to the death of more sailors until a century later, in 1749, when lemon juice was made compulsory in British navy. Quantitative studies put the figure of the sailors who were claimed by this easily curable disease at an average of 5000 each year, but after the discovery of lemon juice these deaths ceased. Almost a million people were claimed by scurvy within two centuries between 1600 and 1800 (Anderson, 2000). A combination of qualitative and qualitative study was used to calculate these figures as well as extend of the disease. From around 1800, there were no more casualties resulting from the disease as lemon and orange juice was adopted by all sailors as prevention for the disease (Dallal, 2000). Throughout the period that scurvy was a menace among sailors, several people tried quantitative, qualitative as well as clinical studies in order to try and contain it but they succeeded when clinical study was emphasized more than the others.

Recall bias can occur in clinical studies especially in cross-sectional as well as case studies whereby the people being examined may be asked to recall their exposure to factors that pose a risk. People who have been victims to a certain disease are able to recall the exposures they may have undergone than those who do not suffer from the disease. A person with a heart condition and who has undergone a heart surgery can recall the exposure he or she had compared to one who does not suffer from the disease (Morabia, 2001). The danger with such biases is that conclusions may be made basing on data that is not reliable. A certain type of analysis may make an underestimation or overestimation about the prevalence of a certain epidemic or disease if it is bases on recall bias.













































Anderson, M, (2000). History of Nautical Medicine. A short history of scurvy. Retrieved


on November 15, 2009. Available at:


Dallas, J, (2000). Cause and Effect. Retrieved on November 15, 2009

Available from;


Eyler, J. M, (2001). The Changing Assessments of John Snow’s and William
Farr’s Cholera Studies. Soz Preventive Med 2001:46 (4): 225-
232. Retrieved on November 15, 2009 from

Morabia A. (2001). Snow and Farr: A Scientific Duet. Soz Preventive Med
2001:46 (4): 223-224. Retrieved on November 15, 2009 from (4) %202234%20Morabia%20Editorial-2.pdf.

Trochim, W, (2006). Research Methods Knowledge Base. Retrieved on November 15, 2009. Available at: