Applications of Epidemiology (Part 2)

Statistics

the science which deals with the collection, classification and use of numerical facts or data bearing on a subject or matter

Vital statistics

- biostatistics

- application of statistical methods and techniques to the study of vital facts, such as those concerning births, deaths, and illnesses, size and characteristics of the affected population

Vital statistics/biostatistics

statistical data which relate to the total number of various kinds of biologic or vital events like births, marriages, illnesses and deaths to the size and characteristics of the affected population

Population

- an aggregate or group of people under study

- ex. All persons living in Cebu City; All females in the reproductive age group

Mid-year population

the population of the area under study as of July 1 (midyear) of a calendar year; considered as a representative of the population of the whole year

Health indicators

list of information which would determine the health for a particular community like population, crude death rate, crude birth rate, infant and mortality rate, neonatal death rates and tuberculosis death rates.

Population at risk

- the population capable of acquiring a disease/s.

- ex. In an outbreak of measles, the population at risk would be those who have not had the disease, who had no immunization against it and those who were exposed to it.

Vital statistics

- generally expressed as vital rates which may be grouped under 3 categories:

A. fertility rate

B. morbidity or illness/sickness rates

C. mortality or death rates

Vital statistics

- serves as an indices of the health of a population based on the births, illnesses and deaths patterns obtained in a community

- ex. A community with a high sickness or death rates can be viewed as a less healthy than the one of low sickness or death rates.

Birth

a coming into being; the act or process of being born

Death

the cessation of all physical and chemical processes that

invariably occurs in all living things.

Marriages

the institution whereby men and women are joined in a special kind of social and legal dependence for the purpose of founding and maintaining a family

Migration

the transfer of one individual from one locality to another locality.

Rates

a relation indicating the number of times a certain event occurs when a certain number of exposures to the risks of occurrence is present in a given period of time.

Morbidity Indicators

- sickness rate

- generally based on the disease-specific incidence or prevalence for the common and severe diseases

Morbidity Indicators

With the use of these indicators, we can partly answer 2 epidemiologic questions "What are the health problems in the area?" and "How many cases occur in the area?"

Prevalence proportion (P)

measures the total number of existing cases of a disease at a particular point in time divided by the number of people at that point in time (if the point in time is the time of examination, then the denominator is the number of people examined)

Prevalence

provides an indication of the magnitude of a health problem and is used for projecting the scope of health services needed by the community

Prevalence Rate

the number of all cases of a specific disease or condition in a population at a given point in time relative to the population at the same point in time.

Point prevalence

When prevalence rates describes the number of people with the disease at a specific point in time

Point prevalence

estimated by data obtained from cross-sectional studies, more commonly known as surveys

Period prevalence

represents the number of existing cases during a specified period or interval of time and include old cases and new cases that appear within the same period

Causes of increase or decrease in prevalence

- changes in local reporting procedures or policies (e.g., change from passive to active surveillance)

- changes in case definition

- increased health-seeking behavior (e.g. media publicity prompts person with symptoms to seek medical care)

Causes of increase or decrease in prevalence

- increase in diagnosis

- new laboratory test or diagnostic procedure

- increased physician awareness of the condition

- increase in reporting (i.e. improved awareness of requirement to report)

Causes of increase or decrease in prevalence

- outbreak of similar disease, misdiagnosed as disease of

interest

- laboratory error

- batch reporting (i.e. reports from previous periods are held and reported all at once during another reporting period)

Incidence Rate

describes the occurrence of new cases of a disease or condition in a community over a given period relative to the size of the population at risk for that disease or condition during that same period, the denominator consists of only those at risk for the disease or condition

Incidence Rate

considered the most sensitive indicator of the changing health of a community because it entails the follow-up of a cohort of disease-free people who are at risk of developing the disease of interest within a specified period of time and thereby captures the fluctuations of disease in the population

Incidence Rate

- valuable for monitoring trends in chronic disease, useful in detecting short-term changes in acute disease such as influenza and etc

- also used in evaluating the effectiveness of health interventions

Attack Rate

- measures the number of new cases of a disease in those

exposed to the disease

- compared and contrasted among those exposed to specific foods to identify the critical food sources or exposure variables

Cohort

a group of people who share common defining characteristics

at-risk group

members of the group are free of the disease but have the potential for developing a particular disease within the specified period of time

Incidence Rate

Numerator: the number of new cases of the event that develop during the period of observation

Cumulative Incidence

can be derived if there are no losses to follow-up and the duration of follow-up is the same so that the denominator is the initial size of the cohort being followed-up

Incidence Density Rate

- computed by using the total person-time at risk for the entire cohort as the denominator

- This happens in the event of loss follow-up

Causes of cohort members being lost in follow-up

- follow-up period is relatively long

- death from other causes

- out-migration

- refusal to continue to participate in the study

time at risk

duration of time during which the person under observation remains disease-free

Specific Morbidity Rates

shows disease rates in specific population groups such as by age, sex, occupation, education, exposure to risk factors, place of residence or combinations of these factors

Specific Morbidity Rates

- can also be computed specifically by seasons of the year

- Epidemiologic questions "Who is affected?", "Where do they occur?", "When do they occur?" can be answered

Descriptive Epidemiology

orienting a disease as to time, place and person characteristics through the various study designs including ecologic studies

Death

most serious outcome of a morbid episode

Mortality Indicators

- provide important information of the health status of the people in the community

- pattern of cause of death indicate most life-threatening diseases that are prevalent in the community

- fails to detect the nonfatal conditions which may not be fatal but are nonetheless widespread

Crude Death Rate

defined as the rate with which mortality occurs in a given population

Factors that affect the level of CDR

- age and sex composition of the population

- adverse environmental and occupational conditions

- peace and order conditions of the place

Crude Death Rate

- the numerator and the denominator pertain to the total population and not to the population subgroups

- expressed as the number of deaths per 1000 population

Specific Mortality Rates

show rates of dying in specific population groups

Cause of Death Rate

- gives the rate of dying due to specific causes

- also a crude rate since the denominator includes the entire population

- can be made specific by relating the deaths from specific cause and group to the midyear population of that specified group

Cause of Specific Death Rate

identifies the greatest threat to the survival of the people, thereby pointing to the need for preventing such deaths

Infant Mortality Rate

defined as the number of deaths of infants under 1 year of age in a calendar year per 1000 live births in the same period

Infant Mortality Rate

- used as an approximation of the risk of dying within the 1st year of life

- not the true measure of risk because not all infants who die in a calendar year were also born in that year

Infant Mortality Rate

Neonatal Mortality Rate and Post neonatal Mortality Rate add up

Prenatal factors, genetic factors

main causes of death among infants less than 28 days old

environmental and nutritional factors, infections

influences the cause of death among infants more than 28 days old (in later months)