I. INTRODUCTION
According to PARAKOYI and OLUBIYI (2009), epidemiology is study of the disease frequency, distribution and determinants of health related states or events in specified populations and application of this study to control of health problems. It is a scientific research discipline concerned with observing, measuring and analyzing health related occurrences in human populations. From the meaning of epidemiology, our discussion will be based on roles of epidemiology in medicine and public health that will be understood by using three epidemiological studies which are descriptive studies, analytical epidemiology and experimental or interventional studies.
II TYPES OF EPIDEMIOLOGICAL STUDIES
II.1 Descriptive Study
In this study we deal with the amount and distribution of a disease within a population by persons, place and time where we focus on these three broad questions necessary to describe the occurrence of a disease.
II.1.1 Person
As our study is based on persons or human being we ask ourselves” who is getting the disease “?
Male or female, the age range, ethnicity, marital status, social economic factors, social class, education, occupation, income level, family variables such as size, type, birth order, maternal age, parental deprivation and personal habits.
II.1.2 Place
We ask ourselves where the disease is occurred. This will answer for region, state, district, local community, towns, village and wards either in the city or rural areas. Boundaries are also considered with precise location.
II.1.3 Time
For more control of an epidemic, the time has the crucial role where we ask when the disease is occurred. This includes the year, season, and day of the week, month and the time of the day. Certain diseases are common during the year for example measles in dry season.
II.1.4 procedures
In descriptive studies we consider the following:
Defining the population to be studied, defining the disease under study, describing the disease by time, place and person, measurement of disease, comparing with known indices and formulation of an etiological hypothesis
II.1.5 ROLE OF DISCRIPTIVE STUDY IN MEDICINE
Used when little is known about the disease
It helps to make a medical diagnosis
Descriptive epidemiology helps to identify problems
It describes health problems in clinical settings
It helps to investigate an outbreak of a communicable disease
It analyzes the reasons for outbreak
It helps to plan a feasible remedy and monitor the effects of the remedy on the outbreak.
It helps to plan effective health services interventions and remedies all depend on accurate community data.
Describes health events
Describes cause and risk factors of disease
Describes clinical pattern of disease e.g. Identify syndromes
Identify control and/or preventive measures
Illustrates potential associations diseases and its causes
II.1.6 ROLE OF DISCRIPTIVE STUDY IN PUBLIC HEALTH
It helps to make a community diagnosis.
identify and describe health problems in a community
To monitor continuously over a period of time the change of health in a community. (For example, the effect of immunization programmes, health education, nutritional supplementation).
To practice surveillance for a specific disease in order to be able to act quickly and so cut short any outbreak
Identify control and/or preventive measures
Patterns of disease occurrence in terms of who gets sick and/or who does not ,where rates are highest and lowest
Data provided are useful for Public health administrators for allocation of resources
Uses measures that represent characteristics of entire populations
We can generate hypotheses for case-control studies and environmental studies
We can target high-risk populations, time-periods, or geographic regions for future studies
To identify health problems to be studied by analytic methods and to test hypotheses related to those problems
II.2 Analytical Study
This is the other major type of epidemiological study that only look at the individuals affected within the population , even though individuals are evaluated in analytical study.
Analytic studies comprises of two types of observational studies
Retrospective or case study: here, we can determine whether or not a statistical association exists between a disease and a suspected factor and if it does, what is the strength of association
Prospective or cohort study: a group of persons are exposed to causative factors while others are not. A follow-up is made in the nearest future to check the proportion of effects on the exposed and the non-exposed and comparison is then made.
II.2.1 Role Of Analytical Study In Medicine
Provides insight regarding the nature, causes, and extent of health and disease
It help to analyze health information regarding to treatment and cure
Used when insight about various aspects of disease is available
Evaluates the causality of associations
We can aggregate cases from disparate sources to generate hypotheses and describe new syndromes Example: hepatitis, AIDS
Good for identifying prevalence of common outcomes
It Helps to show characteristics of the disease and illness
It Helps to establish modes of transmission
II.2.3 Role Of Analytical Study In Public Health
Provides information needed to plan and target resources appropriately
It analyze outcomes in relation to age, time, utilization of services, or exposures
Data represent average exposures rather than individual exposures, so we cannot determine a dose-response relationship
Caution taken to avoid drawing inappropriate conclusions regarding study findings
Quantifies linear relationship between exposure & disease
Measures disease and exposure simultaneously in a well-defined population
Represents value present at initiation of disease
It helps to establish distribution of disease by the time, place and person
It helps to measure morbidity which refers to the presence of disease in a population and mortality which refers to the occurrence of death in a population
It helps to determine disease frequency in the population which is expressed in Rate (Frequency of defined events in specified population for given time period) and allow comparison between two or more populations of different sizes or of a population over time
It helps to compute disease rate including the number of persons at risk, number of persons with disease which are required to calculate rate (Rate = persons with disease over population at risk)
Prevalence and Incidence in analytical study help us to know existing and new cases of disease in the population during a defined period.
In analytical study the Incidence rate is helpful in measuring the probability of the event among persons at risk (Incidence Rates =number of new cases in given time times constant over specified population at risk,( kanupriya chaturvedi,2013)
During analytical study the relationship between an outcome and certain factors (e.g., age, sex, race, smoking status, etc.) is established
Used to guide planning and intervention strategies
To evaluate trends in health and disease and allow comparisons among countries and subgroups within countries
II.3 THE EXPERIMENTAL/INTERVENTIONAL STUDIES
This is a study in which one group deliberately subjected to an experience, is compared with a control group which has not had a similar experience. The use of experiments in this study is done with ethical considerations. It usually involves selection of an individual or communities. The principle of conducting experimental trials is that under the control of the investigator, some system are subjected to manipulation, creating an independent variable whose effect is then determined by the measurement of subsequent events or outcome. This is known as dependent variable.
II.3.1 Roles Of Experimental/Interventional Studies In Medicine
It is helpful in testing a potential intervention or treatment
It is the most reliable way to test the effectiveness of a treatment or intervention.
Secondary prevention that help to make therapeutic interventions to alleviate symptoms, prevent recurrence or decrease risk of mortality. An example: chemotherapy for breast cancer.
It helps to compare patients on the new treatment with another group of patients receiving either standard treatment to see effectiveness of new treatment
II.3.2 Roles Of Experimental/Interventional Studies In Public Health
It helps to quantify the effect of an exposure (e.g. environmental, genetic or behavioral) on the outcome
Interventions can be classed as primary prevention that helps to reduce the risk of exposure an example: smoking cessation intervention.
It helps to make a trial which is used as an experiment to test an intervention
It helps to compares a group of people with a condition (the cases) with a similar group of people who do not have the condition (the controls).
It is useful for describing epidemiological study designs.
It is used to investigate patterns of ill-health, generate and test hypotheses for the causes of ill-health,
It is helpful to take action to prevent illness,
It is used to promote health, and finally to evaluate existing health services and Public Health interventions.
III. CONCLUSION
Epidemiology is the cornerstone of Public Health. It employs rigorous methods and a quantitative approach to study the health of populations rather than individuals. Epidemiological methods are used to identify the causes of poor health, measure the strength of association between risk factors and disease, and evaluate interventions and monitor changes in population health over time. In short, epidemiology provides the necessary information for Public Health actions and decisions to be taken.
IV. REFERENCES
1. BRAY I. and REGMI, K.2016. Epidemiology and Public Health Intelligence. Frenchay Campus. UK.
2. CHATURVEDI, K. 2013.Descriptive Epidemiology. University of Philadelphia.USA.
3. PARAKOYI, B. and OLUBIYI, K. S .2009.Epidemiology in nursing. University of Nigeria. NIGERIA.