Epidemiology is the study of disease occurrence and transference in human population wherein its focus involves the distribution and determinants of disease. It is frequently used in public health as a systematic and scientific approach for understanding diseases and health problems (Waning & Montagne, 2001 p.1). The essential aim of epidemiology is to establish awareness of disease causation and improve the general health conditions of the public (Woodward, 2005 p2).
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The paper discusses various epidemiologic study designs specifically, cross-sectional, retrospective, descriptive, prospective or cohort and randomized clinical trial or also known as randomized controlled trial. Detailed explanation and comparisons are included in the entire discussion.
In a cross-sectional study, the subjects are chosen irrespective of their exposure or disease status. Exposure and disease are being measured importantly at the same point in time. Another reason for this is that the time organization between the start of exposure and the start of disease is impossible to be hypothesized. Moreover, the data results from the cross-sectional study can be treated also as data from cohort study or as data from case-control study (Monson, 2001 p.59). Cross-sectional study involves the study of subjects in the population at the time of ascertainment or a representative sample of all such persons, including those who have the disease, and that has an objective limited to describing the population (Rothman & Greenland, 1998 p.75). The possibility of conjuring the disease is measured in this study; but those who possess the actual conditions are ones involved.
Cross-sectional studies do not include causative factors; however, it utilizes prevalence data as its etiologic inferences (p.75). However, the difficulty in evaluating data in a cross-sectional study is to decide whether the exposure led to the disease or the disease lead to the exposure (Monson, 2001 p.59). In fact, the collection of data in cross-sectional manner is not actually the defining characteristics of the cross-sectional study but the inability to formulate the exposure-disease time organization is its sole defining characteristic (p.60).
The design of retrospective utilizes population based case study that possess limitations to geographical, hospital based wherein the subjects are the admitted patients and lastly, group based wherein studies are based on local epidemics. This type of epidemiologic design is most commonly conducted since their results have immediate applications to the enhancements of health promotion and prevention (Miller, 2002 p.287). A case-control study is sometimes referred to as a retrospective study because data on the factor of interest are collected retrospectively; however, there are cases wherein subjects encounter varying inconsistencies (Smoller, 2004 p.9). The design detects a number of people with the disease under the study criteria, which is known as the case. After such, the selection of those subjects free from the disease, called controls, are involved. The cases and controls are then investigated to see which risk factors differ between them (Woodward, 1999 p.243)
Retrospective studies are utilized in determining the differentiation of well group and ill group in terms of exposure proportion to specific disease etiological agent, risk factors or the pathogen. The defining characteristics of retrospective study are its comparison of the groups concerning the presence of traits, characteristic or factor that result from past activities or experiences (Timmreck, 2002 p.237).
Descriptive epidemiology is concerned with the distribution of disease, including consideration of what populations or subgroups do or do not develop a disease, in what geographic locations it is most or least common, and how the frequency of occurrence varies over time. The design study of descriptive epidemiology involves more on qualitative provision of description of disease distribution of health-related stares and phenomena by person, place, and time. This design aids in the familiarization of data, identification of community health problems, defines the at-risk population, and lastly, analyzes the traces of disease determinants (Timmreck & Merril, 2006 p.80).
Descriptive design are further subpided into four categories of study specifically, ecologic studies, case reports, case series, and cross-sectional surveys. The ecologic study focus mainly on population analysis while the other designs centers on inpidual analysis. Unfortunately, the negative side of descriptive design is its limitation to test hypothesis (p.80). The descriptive studies are useful for hypothesis generation, but not for hypothesis testing. The case-control and cohort designs provide more persuading proofs to test particular hypotheses (Greenberg, p.203).
Cohort or prospective design is pided into two categories of implementation namely prospective cohort study and historical cohort study. The prospective cohort study deals with the assembling of present and followed by future time frame while historical cohort study identifies from past records and followed forward from that time up to the present (Fletcher & Fletcher 2005 p.82).
The difference of case-control or retrospective from cohort studies is that all the relevant phenomena, such as disease and exposure, have already occurred when the study starts while, in cohort studies, the exposure has occurred but the disease has not yet been present. However, there is one exemption to the rule wherein study is done through records review. Prospective design refers to the study group following forward in time from exposure to disease in contrast to the case-control design that proceeds backward in time from disease to exposure (Hebel & McCarter, 2006 p.115).
The study design of randomized clinical trial is another type of prospective experiment that analyzes the comparison of one or more plan of actions against a control group for the purpose of knowing the effectiveness of the interventions proposed. This design utilizes clinical trials in order to formulate the comparison of health interventions or measures given (Smoller, 2004 p.141).
However, this design is faced with several ethical dilemmas involving clinical trials and experimentations. The ethical violation involves the utilization of humans as the subject for clinical trials.
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