BIO 550 Week 3 Discussion Questions
BIO 550 Week 3 Discussion Questions
DQ1 Describe the key features of descriptive and analytic epidemiology. How are the two used in conjunction with one another?
DQ2 What is a clinical trial? Support your description with literary rationale. Why do you believe clinical trials are beneficial?
BIO 550 Week 3 Discussion Questions
The experimental method is the most powerful tool in defining the etiology of recurring developmental anomalies. The basic approach of the applied experimental method is to take one or two of the most likely hypotheses and test them one at a time on part of the herd, using other untreated animals as controls. It is important to randomly select individuals to remove sample bias. If the herd is large, it may be divided into a number of groups, allowing for the simultaneous testing of more than one hypothesis, but this depends on the prevalence of the anomalies. For example, the herd could be divided into four groups: old animals with access to suspected toxicant; young animals with access to suspected toxicant; old animals with no access; and young animals with no access. Developmental anomalies of low prevalence require larger sized groups. Usually, a prevalence of 25% will allow a group size of 50 animals, depending on the variability of expression of the defect.
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Records at the termination of the experiment (the next calving season) should include reproductive problems, abortions, stillbirths, and anomalies. Statistical tests to determine if the differences between test and control groups are statistically significant can be used. A statistical difference in the prevalence of anomalies between the two groups is evidence that the risk factor tested is the cause of the anomalies. It should be remembered that lack of statistical significance does not necessarily “disprove” associations among groups, as this often occurs in low prevalence situations with inadequately-sized test and control groups. With proper randomization and care in treating the two groups similarly, a statistical difference in the prevalence of anomalies between two groups is evidence that the risk factor tested is the cause of the anomalies.
In summary, identification of the etiology of developmental anomalies is often extremely difficult, for many reasons. First, defective development alone often does not give clues to a specific cause. Second, specific teratogens such as viruses, plants and toxins, often cannot be demonstrated at the time of expulsion of the defective fetus, or even after intensive pathological and toxicologic investigations. Third, except for certain chromosomal aberrations, hereditary factors are recognized only when they occur in characteristic intra-generational familial frequencies and patterns. Therefore, when a cause cannot be demonstrated, attempts to determine patterns of occurrence must be undertaken. The method described provides a step-wise protocol to determine etiology.