Comparison Of Epidemiological Study Designs

Observational Epidemiological Studies

Discuss about the Comparison of Epidemiological Study Designs.

A study design follows a specific protocol and methodology to reach specific interpretations to confirm hypothetical concepts into operational ones. Study design are framed keeping in mind the specific requirements, limitation and desired outcomes of the study. Several qualifying criteria are assessed before a design is implemented to conduct a study. Epidemiological studies are quantitative studies that identify relations between exposures and outcomes of a particular disease. Achieving this goal with least error is the indicator of an efficient Study Design. Epidemiology is the branch of Medical Science that deals with the study of causes, incidence, distribution and measures to control a disease in a defined population. Three key terms are of utmost relevance in this regard: Exposures, Outcomes and Cofounders (Fletcher et al., 2012). The researcher identifies the exposures and cofounders and analyses the consequent outcomes of a disease, to reach to relevant conclusion, often aimed at proposing a preventive measure. Several classifications of epidemiological studies are possible depending on specific factors. The one most extensively used is based on the role and control of the researcher over the study parameters (Szklo & Nieto, 2012). In Observational Studies, the researcher has least control over the study situation; he/she merely studies the trend and etiology of a disease. Experimental studies are designed to apply a certain level of intervention to the affected population and observe the consequent results. This essay aims to compare and evaluate various features of two such epidemiological study designs: one Experimental and one Observational utilised in two different research studies on chronic diseases.

Observational epidemiological studies are conducted to determine, if any, the association between adverse health-related issues and certain potential causative factors. It aims to describe the occurrence of a disease by time, place and person. Observational studies have several classifications including Cohort, Case-control, Cross-sectional and Routine Data-based studies (Robertson, 1998). In Cohort studies a cohort or fixed population is selected, which is exposed to a certain factor, and then the whole population is studied. Subjects with and without a specific disease is identified and prior exposure to risk factors are analysed in Case-control studies. In Cross-sectional studies a set of individuals are selected from a predefined population and information is collected at a particular time to assess both exposures and outcomes. In Experimental Epidemiological Studies, the researcher intervenes with the treatment of the disease to study the effect of doing so. Experimental designs include Controlled and Uncontrolled Trials. Controlled Trials consist of a control group, which does not experience any intervention for comparison with the intervention group. Uncontrolled Trials do not have such control groups. The allocation of different study subjects to the control and the intervention group are done by random sampling to avoid any kind of bias on part of the investigator or the researcher. Interventional Studies can be Clinical trials as well as Filed trials. A clinical trial evaluates different treatment methods of a disease or a condition and is generally conducted in a medical set-up. Field trials are conducted in a specific location or community to assess risk factors in reducing the incidence of a disease. Selection of a suitable study design is completely dependent on the discrete objectives and purpose of the study. There are specific advantages and disadvantages associated with the different study designs, which is essential during the selection procedure.

Experimental Epidemiological Studies

Two studies on chronic diseases that are selected to serve the purpose of this essay are Additive effects of glycaemia and blood pressure exposure on risk of complications in type 2 diabetes: a prospective observational study (UKPDS 75) (Stratton eta al., 2006) and Nutrition intervention is beneficial in oncology outpatients receiving radiotherapy to the gastrointestinal or head and neck are (Isenring, Capra & Bauer, 2004).

The first of the two chosen studies is an Observational Epidemiological Study conducted on 5,102 subjects in UK who fulfilled the inclusion criteria. The authors aim to measure the effects of glycaemia and systolic blood pressure exposure on the incidence of type 2 diabetes complications. Patients in the age group of 25 to 65 years of age who are newly diagnosed with type 2 diabetes and fasting plasma glucose level of >6.0 mmol/l were selected. Patients with severe vascular disease, a myocardial infarction or stroke or any other major systemic disease were excluded from the study group. The study tries to assess if there is any additive or individual relation between type 2 Diabetes complication and a prior history of hypertension and hyperglycaemia in the selected patient group. The Type 2 diabetes has been an epidemic and controlling the post disease complications has been an absolute necessary presently. Controlling the glycaemic levels of patients by specific interventions has been a topic of extensive study in order to manage the complications generally related to the chronic disease. Interventions to control the glucose levels of patients close to nondiabetic levels have shown to have beneficial effects (Nathan et al., 2009). Studies also clearly state the relation between type 2 diabetes complications and hypertension and obesity (Colosia, Palencia & Khan, 2013). The study qualifies as a cross sectional study as the authors observes and collects data from a selected group in the population over a particular time period to assess both the exposures and the outcomes of the disease. The authors aimed to find whether the number of patients who eventually developed some kind of type 2 diabetic complication had lower or higher values of blood glucose level and systolic blood pressure. Hence, the selected study design is apt for conducting this study. The study results show independent as well as additive association between hypertension and hyperglycaemia. The authors conclude that the incidence of type 2 diabetes related complications could be effectively avoided by controlling the two risk factors viz. hypertension and hyperglycemia. The study results and interpretations have significant clinical implications.

Advantages and Disadvantages

The second study chosen is an Experimental Epidemiological Study that aims to evaluate the effect of nutritional interventions in outpatients who are undergoing radiotherapy to their GI tract or neck and head region. The authors aimed at comparing the impact of nutritional intervention on the selected population of patients by comparing the intervention group with a control group, which received usual care. The population of outpatients, which fulfilled the exclusion criteria of at least 20 fractions of radiotherapy, were grouped by random sampling. Hence, the study can be classified as a Controlled Clinical Trial. Different parameters like body weight, body composition, nutritional status, quality of life and physical function were measured for both the groups. Patients undertaking radiotherapy are found to bear various side effects. Radiotherapy on the head and neck region often causes dryness of mouth and consequently may reduce oral intake of food, resulting in loss of body weight (Vissink et al., 2003). GI tract radiotherapy may cause nausea, vomiting and diarrhoea leading to nutritional insufficiency. Although nutritional support has been recommended to reduce physiological side effects of radiotherapy but very few studies addressed the issue. This provides the rationale for conducting the study and utilising the mentioned study design. The study concludes that there was significant improvement in the intervention group in terms of reducing weight loss, deterioration in nutritional status, quality of life and physical function of the concerned patients. The study results are relevant for practical application. Patients undergoing radiotherapy of GI tract and head and neck region, who are at risk of malnutrition, should be provided with sufficient nutritional intervention during as well as post radiotherapy sessions.

There are certain advantages and disadvantages of the two kinds of studies that have been employed in the mentioned studies, as in every study designs or models. Cross-sectional observational epidemiological studies are advantageous in a sense that they address both the outcomes and exposures of a disease for long durations of time. It can provide relevant background information about the disease impact on a population or community and formulate health care services accordingly. On the contrary, common disadvantages are that it cannot indicate a cause-effect relationship of a disease and quantify a risk factor. Short duration disease may be overlooked in cross-sectional studies. it is best applied for chronic long duration disease like hypertension, diabetes, cancer and so on and so forth.

Experimental Epidemiological studies that include clinical trials provide strong evidence of the effects of interventions on a disease to support an already proposed hypothesis regarding the same issue. Here, the effects of intervention can be precisely measured as the intervention group results are compared to a control group results, outlaying significant difference between the two if any. The investigator has control over the environment of the study as opposed to observational studies. These types of studies can infer about the safety and effectiveness of a treatment or intervention procedure. Randomized sampling of the population while dividing the same into intervention and control groups evades any possibility of bias in the study results and consequently incorrect interpretation. Conversely, large trials may reduce the quality of statistical analysis tools and long-term follow up of the subjects. Possible ethical considerations need to be addressed before conducting clinical trials. 

In conclusion, the studies chosen to compare the two different study designs successfully meet the objectives and have practical significance. The rationale behind choosing the particular study designs was sound and effective in reaching their goals. 

References

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Colosia, A. D., Palencia, R., & Khan, S. (2013). Prevalence of hypertension and obesity in patients with type 2 diabetes mellitus in observational studies: a systematic literature review. Diabetes Metab Syndr Obes, 6(1), 327-38.

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Isenring, E. A., Capra, S., & Bauer, J. D. (2004). Nutrition intervention is beneficial in oncology outpatients receiving radiotherapy to the gastrointestinal or head and neck area. British journal of cancer, 91(3), 447-452.

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Stratton, I. M., Cull, C. A., Adler, A. I., Matthews, D. R., Neil, H. A. W., & Holman, R. R. (2006). Additive effects of glycaemia and blood pressure exposure on risk of complications in type 2 diabetes: a prospective observational study (UKPDS 75). Diabetologia, 49(8), 1761-1769.

Szklo, M., & Nieto, J. (2012). Epidemiology. Jones & Bartlett Publishers

Vissink, A., Jansma, J., Spijkervet, F. K. L., Burlage, F. R., & Coppes, R. P. (2003). Oral sequelae of head and neck radiotherapy. Critical Reviews in Oral Biology & Medicine, 14(3), 199-212.