Epidemiology and Biostatistics
Epidemiology
I-Definition
Epidemiology is a scientific discipline whose object is the study of the distribution of health problems in a population and the role of the factors that determine it.
Epidemiology studies groups of people, not individuals. The analysis focuses on healthy individuals and individuals affected by disease.
II-THE OBJECTIVES OF EPIDEMIOLOGY
Epidemiology allows us to collect, interpret and use information on health problems. Its objectives are the promotion of health and the reduction of health problems. To do this, it is necessary to:
1- detect an epidemic,
* identify a new disease,
* describe the risks to which a population is exposed in a given environment.
2-Search for the causes of the conditions,
3-Assess the importance of a problem,
4-Formulate hypotheses and verify them,
5-Evaluate care (diagnostic and screening techniques, treatment, public health programs),
6-Evaluate progress through the fall in mortality or morbidity.
II-1- DESCRIPTIVE EPIDEMIOLOGY
The purpose of descriptive epidemiology is the description of a health phenomenon in
a population (frequency, variations) based on the characteristics of this population
and parameters such as time and space.
It is necessary to measure the importance of a health problem and raise
etiological hypotheses (risk factors for the occurrence of this disease).
Example: we wish to study the evolution of mortality from breast cancer between 1980 and 2012 in ALGERIA.
II.2 ANALYTICAL OR ETIOLOGICAL OR CAUSAL EPIDEMIOLOGY
Its aim is to research the causes of diseases and the factors or markers of
risk influencing their occurrence within a population. It thus makes it possible to establish
causal relationships between exposure to a risk factor or marker and disease.
Risk is defined as the probability of a given event occurring.
Risk factors increase the likelihood of developing the disease.
However, it is possible to act on exposure to these risk factors:
Example: tobacco, alcohol…
II-3- EVALUATIVE EPIDEMIOLOGY
Evaluative surveys study prevention or treatment actions.
Example: Evaluate the annual influenza vaccination campaign within the Center
Hospitalier X with health professionals working in maternity.
III-THE DIFFERENT TYPES OF EPIDEMIOLOGICAL STUDIES
There are two main types of studies depending on whether it is an experimental study or
No.
III.1 EXPERIMENTAL STUDIES
The researcher intervenes on the exposure status of the subjects. He can intervene on
● the exposure factor(s),
● the time of exposure,
● exposed persons.
Firstly, the groups will be monitored and then compared with each other.
In practice, the conduct of experimental studies is often limited due to ethical constraints.
- The principle of randomization
The study is said to be randomized if the assignment of subjects to one group or another is drawn randomly. It is therefore chance that determines the subject’s membership in a group. Thus, only the group to which the subjects belong seems to be able to differentiate the subjects from each other.
Randomization helps limit study bias
Randomized studies or trials are qualified:
-open when the treatment is known to all,
-single blind when only the patients are unaware of the nature of the treatment,
-double-blind when patients and doctors are unaware of the nature of the treatment.
III-.2 NON-EXPERIMENTAL STUDIES
They are also called observational studies.
They can be descriptive or etiological. The researcher will observe reality
without intervening in the conditions of exposure of the subjects.
Descriptive studies are:
III.2.1 Prevalence studies
Prevalence studies allow us to observe the frequency of occurrence of a
health phenomenon, in a population, at a specific time. These are surveys
cross-sectional. The information collection is carried out over a short period, “on a given day”.
The concept of patient monitoring over time is absent. It is a “static” indicator
of morbidity.
III.2.2 Impact studies
Incidence studies require the observation over a given period of time of one or more
groups of subjects to measure changes in the health status of populations. This involves
longitudinal studies.
IV-Cohort studies
A cohort is a group of subjects followed over time. Cohort studies are also called exposed/unexposed studies. In practice, two groups are established:
subjects exposed to the risk factor
The two groups will be followed (longitudinal studies) and then compared with each other.
We will speak of a historical cohort if the occurrence of exposure to the factor(s) and the disease has already taken place at the time the researcher begins his investigation.
V-CASE STUDIES
Two groups of subjects will be compared:
● Sick subjects: “the cases”
● Non-sick subjects: “witnesses”
The information gathering is always retrospective in this case. The groups are then
compared. Cases and controls should be selected from the same population.
characteristics of the “control” group must be as close as possible to the “case” group
” The only observable difference between the groups should theoretically be the absence of
signs of the disease.
Bio statistics
I-Definition
Biostatistics is the application of statistical processing to biological data. It is an interdisciplinary field that combines biology, computer science and statistical mathematics.
In clinical research, biostatistics includes the design of protocols, the compilation and analysis of collected data, and the interpretation of results.
II-OBJECTIVES OF BIOSTATICS
*to acquire and perfect knowledge of the main concepts relating to the use of
statistical methods,
*to solve empirical questions through the use of statistical tests,
* to master and complete the basic notions of statistics with a view to applying them to examples specific to the biological sciences, taken in their general sense (biology, medicine, pharmacy, ecology, etc.)
* to apply these concepts and methods to biological data using simple software
* to use statistical software and learn how to read their results.
III-Statistics
The goal of statistics is to extract relevant information from a list of numbers that is difficult to interpret by simple reading. Two main families of methods are used depending on the circumstances. Nothing prevents them from being used in parallel in a concrete problem, but we must not forget that they solve problems of totally distinct natures.
1-Descriptive statistics
Descriptive statistics is a set of methods for describing and analyzing phenomena that can be counted and classified. Its purpose is to describe, not to explain.
1-1-Basic Concepts
Observations are the source of statistical information. Before starting the study, it is necessary to have the study set and the criteria of the numerical description
.*. The sets studied are called populations.
*. The elements of the population are called individuals or statistical units.
.*. A subset of the population is a sample and its size corresponds to its cardinality
*. The criteria studied constitute characteristics; and a characteristic makes it possible to determine a partition of the population. Example
We summarize the different concepts in this example:
-Population: all employees of a factory.
-Individual: each employee of the factory.
-Character: salary, marital status, number of children, etc.
-The modalities of the character: married, single, divorced and widowed are the modalities of marital status, for example
2-Mathematical statistics
This branch of mathematics, closely linked to probabilities, is essential to validate the hypotheses or models developed in inferential statistics. The mathematical theory of probabilities formalizes random phenomena. Mathematical statistics is devoted to the study of random phenomena that we know through some of its realizations.
3-Statistics in social sciences
Statistics are used in most social sciences . They have a common methodology with, however, certain specificities depending on the complexity of the object of study.
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Epidemiology and Biostatistics
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