EPIDEMIOLOGY IN ENGLISH
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EPIDEMIOLOGY-
} Epidemiology is defined as "The study of the
distribution and determinants of health related states or events in specified
populations, and the application of this study to the control of health
problems.
} Epidemiology also includes study of the health
services used by the population, and to measure their impact. Epidemiology,
like public health itself, is often more concerned with the well-being of
society as a whole, than with the well-being of individuals.
COMPONENTS OF EPIDEMIOLOGY-
} There are three main components of epidemiology.
} 01. Disease frequency;
} 02. Distribution of disease; and
} 03. Determinants of disease.
} 01. Disease frequency - The basic measure of disease frequency is a rate or ratio. These rates are
essential for comparing disease frequency in different populations or subgroups
of the same population in relation to suspected causal factors. Such
comparisons may yield important clues about causes of the disease.
} 02. Distribution of disease- The study of how the disease is distributed in
human populations is an important component of epidemiology. It is the study of
pattern of disease occurrence in a community. The patterns may lead to the generation
of hypotheses about causative factors or
risk factors.
} 03. Determinants of disease- A main feature of epidemiology is to test
aetiological hypotheses and identify the underlying causes (or risk factors) of
disease. This requires the use of epidemiological principles and methods.
OBJECTIVES OF EPIDEMIOLOGY-
} Epidemiology has three main aims:
} To describe disease and other health related event
patterns in human populations.
} To identify the causes of diseases and other health
related events (also known as aetiology).
} To provide data essential for the management,
evaluation and planning of services for the prevention, control and treatment
of disease and other health related events.
MEASUREMENTS IN EPIDEMIOLOGY-
} The measurements in epidemiology are many few of them
are grouped as :
} a. Measurement of mortality
} b. Measurement of morbidity
} c. Measurement of disability
} d. Measurement of natality
TOOLS OF MEASUREMENT IN EPIDEMIOLOGY-
The basic tools of measurement in epidemiology are :
} 1. Rates- A rate measures the occurrence of some
particular event (disease or death) in a population during a given time period.
It is expressed as per 1000 or per 10000 or per 100000. Example crude death rate.
} 2. Ratios- It expresses a relation in size between two
random quantities. Broadly, ratio is the
result of dividing one quantity by another. It is expressed in the form of:
x: y or x/y
Example- sex-ratio, doctor-population ratio.
} 3. Proportions- A proportion is a ratio which indicates the relation in magnitude of a
part of the whole. The numerator is always included in the denominator. A
proportion is usually expressed as a percentage.
MORTALITY RATES-
} Crude Death Rate- It is defined as "the number of
deaths (from all causes) per 1000 estimated mid-year population in one year, in
a given community or place“. The crude death rate is calculated from the
formula:
CDR= (No. of deaths during the year/mid year population) X 1000
} Specific Death Rate- when death rate is specific to a
condition than it is known as specific death rate. It may be disease specific,
age specific or specific to any other variable such as sex, housing, class etc.
SDR = (No. of specific deaths during the year/mid year population) X 1000
} Case fatality Rate- Case fatality rate means the
killing power of a disease. Case fatality rate is normally used in acute
infectious diseases. It is defined as no. of deaths due to a disease per 100
cases of the disease.
CFR = (No. of deaths due to a disease/total no of cases of same disease) X 100
} Infant mortality Rate- infant mortality rate is
defined as the ratio of deaths under 1 year of age in a given year to the total
number of live births in the same year. It is measured by the this formula.
IMR = (No. of deaths of infants /total no of live births during the year) X 1000
} Maternal mortality Rate- maternal mortality rate is
defined as the ratio of deaths of mothers due to pregnancy related causes the
total number of live births in the same year. It is measured by the this
formula.
MORBIDITY RATES-
} Incidence Rate- "the number of NEW cases of a
particular disease occurring in a defined population during a specified period
of time". It is given by the formula :
Incidence rate = (No. of new cases of a disease during the given period of time /population at risk during the period) X 1000
} Prevalance -
The term "disease prevalence" is defined as all current cases of a
disease (old and new) existing at a given point in time, or over a period of
time in a given population
prevalance rate = (No. of all cases new and old of a disease during the given period of time /population at risk during the period) X 1000
DISABILITY
RATES-
The commonly used disability rates fall into two
groups:
(a) Event-type indicators and (b) person-type
indicators
(a) Event-type disability rates
i) Number of days of restricted activity
ii) Bed disability days
iii) Work-loss days (or school-loss days) within a
specified period
(b) Person-type disability rates
i) Limitation of mobility: For example,
confined to bed, confined to the house, special aid in getting around either
inside or outside the house.
ii) Limitation of activity: For
example, limitation to perform the basic activities of daily living (ADL)
eating, washing, dressing, going to toilet, moving about & limitation in
major activity, ability to work at a job, ability to housework, etc.
NATALITY RATES-
} crude birth rate - Birth rate is the simplest natality
rate and is defined as "the number of live births per 1000 estimated
mid-year population in a given
year". It is given by the formula:
crude birth rate = (No. of live birth in an area during the year /mid year population ) X 1000
} General fertility rate - It is defined as the
"number of live births per 1000 women in the reproductive age-group (15-44
or 49 years) in a given year“ .It is given by the formula:
General fertility rate = (No. of live birth in an area during the year /mid year female population of reproductive age ) X 1000
EPIDEMIOLOGICAL METHODS-
} Basic epidemiologic methods are based on careful
observation and use of valid comparison groups to assess whether what was
observed, such as the number of cases of disease in a particular area during a
particular time period or the frequency of an exposure among persons with
disease, differs from what might be expected. Main methods are observational
studies and experimental studies. These are also known as
epidemiological studies or research studies.
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