Measure of Frequency in Epidemiology

Every now and then, there are several diseases that occur around the world. A disease may only be present in a certain population like ebola. This disease spread in the African region and did not spread throughout the world. Instead, it occurred frequently in the same area among the same people. In order to reduce such outbreaks around the globe and prevent the spreading of such diseases, epidemiology is used. In simple terms, epidemiology describes the way diseases occur in the population as well as the frequency of their occurrence. We will try to gain a comprehensive understanding of epidemiology in this article.

What is Epidemiology?

An epidemiologist studies and identifies health and disease conditions, the causes and possible controls of diseases, as well as their incidence, distribution, and determinants. In summary, the study refers to scientific, systematic, and data-driven research when we break down this complex definition into the simplest terms possible. The distribution of disease describes the frequency and patterns of occurrence. 

Determinants are factors that cause diseases to spread and risk factors for their spread. In comparison with other health-related and medicine-related studies, epidemiology is unique in that it involves not just studying the occurrence of varietal diseases, but also assessing other health-related incidents that occur within a population.

Study of Populations

The main studies of population frequencies should be understood before one decides which measure of disease frequency one should use. There are two types of studies of the population that are dynamic population and cohort. Dynamic populations, known also as dynamic cohorts or open cohorts, are conceptually similar to dynamic populations; consistently, all subjects who drop out of a study for any reason are replaced by new participants. By contrast with dynamic populations, cohorts are permanent groups whose membership cannot be added once the cohort has been identified and follow-up has begun.

Prevalence

Prevalence measures how many people in a population suffer from a specific disease, and could be interpreted as a measure of a disease’s severity. It expresses how many people (proportion) have that disease among a population:

Prevalence = Number of subjects having the disease at a time point/Total number of subjects in the population

When examining the prevalence of a disease in a particular population, it is useful to see how burdensome the disease is. This does not just refer to the economic burden of the disease; it can also refer to anxiety, morbidity, quality of life, or other factors. Investing in health care can be a wise choice when decision-makers know how much money to invest. In general, there is a need for dialysis facilities when there is a large number of patients with end-stage renal disease (ESRD).

Incidence

Unlike prevalence, which reflects the number of people who are currently suffering from a disease, incidence represents the number of people who are currently developing it, which is expressed as a risk or as an incidence rate.

Risk

An individual’s risk is a statistical estimate of how likely he or she is to develop a given disease, or other health outcomes, during a given follow-up period. The following calculation can be accomplished by dividing the total number of subjects over that period by the number of subjects who developed the disease over that period:

Risk = Number of subjects developing the disease over a time period/Total number of subjects followed over that time period

Incidence Rate

Disease incidence is also expressed as a measure of frequency called the incidence rate. The number of individuals developing a disease can be calculated by dividing the total time at risk for all people to get the disease by the number of such individuals. Instead of just including a number of subjects as a denominator, this formula includes a measure of time. Thus, we should see the incidence rate of a specific event as an instantaneous concept:

Incidence rate = Number of subjects developing the disease/Total time at risk for the disease for all subjects followed

Difference between Incidence and Prevalence

Figures illustrate how factors affecting prevalence include how many incidents occur, how many deaths occur, and how many recoveries occur. Assuming that the disease is in a steady-state, the prevalence will be equivalent to the product of the incidence rate and the mean duration. An example of this is tetanus and end-stage renal disease. Tetanus, which is caused by Clostridium tetani, is a rare, acute, and usually fatal disease. It often results in quick death due to rapid death. ESRD, on the other hand, is relatively rare, but at least in developed nations, it has a better survival rate than tetanus.

Conclusion

In addition to determining the associations between exposures and outcomes, measures of disease frequency can also be computed. In order to study the effects of exposure, the disease frequency of exposed subjects can be compared to the disease frequency of unexposed subjects. An association between exposure and disease can be estimated from the comparison of these frequencies. By comparing two populations’ disease frequency, you can determine the relative risk of one population (relative risk) versus another (risk difference) as well as the frequency difference that indicates how frequent disease is in one population compared to the other (risk difference). Using epidemiology and its corresponding measure of frequency, we examined this article.