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Analysis of Observational Studies using Frequency Measures

The ratios, proportions, and rates are used in epidemiology to describe the birth, disease and death. The birth rate, mortality rate and the prevalence or incidence rate of a disease can be calculated using the data derived from the observational studies.

It is vital to consider the concept of ‘confidence interval’ because of error of random sampling in observational studies and the outcome achieved may differ from the reality, because of chance. Confidence interval will be calculated to assess or evaluate the possible impact of this sampling error. The most commonly used confidence intervals in health-related research are 95% intervals. For Relative Risk (RR), the null value or ‘no-effect’ is 1.0. 1.0 RR indicates that the two groups being compared do not differ. If both ends of the confidence interval are less than 1.0, then it indicates an inverse relationship between exposure and outcome; similarly a positive relationship exists if both ends of the CI are greater than 1.0. However, if the CI includes the null value, i.e. the upper limit is greater than 1.0 and the lower limit is less than 1.0, then a researcher may not disclose the likelihood that the real RR is 1.0, and thus the relationship do not exist between exposure and outcome [3].

Cohort study: incidence rate, relative risk and mortality rate

Data from cohort study can be evaluated and/or analyzed using incidence rate, relative risk and mortality rate. Mortality rate is regarded as a descriptive frequency measure while incidence rate and relative risk as measures of comparative effect [6]. Cohort study analysis used the ratio of the rate of disease in the exposed group compared with the rate in the unexposed group.

Incidence rate

In epidemiology, incidence simply means the occurrence of new cases of disease, for example, new cases of Ebola disease, Lassa fever, or injury in a population during a specified period. The incidenceof a particular disease measures how quickly or frequently the disease of interest is been developed by people. Unlike prevalence, incidence considers only new cases, and it has a unit. In order to measure the incidenceof a disease, a cohort study should be conducted. The study will include participants who are at risk of developing the disease of interest. Then they should be followed to determine those that truly developed the disease. Incidence rate is one of the approaches of measuring the frequency of disease in a population. Therefore, the incidence rate of a disease measures the frequency of the disease occurrence in a population over a specified period. Incidence rates are subject to change over time, from disease to health, therefore the period of the cohort need to be specified.