Demography, Vital Statistics, and Epidemiology

Demography, Vital Statistics and Epidemiology

• This chapter focuses on demography, epidemiology, vital statistics, and their relevance to community health.
• Empirical data will support community diagnosis and community development plans.
• The chapter includes lessons on Demographic Data, Vital Statistics, and Epidemiology.
• The lessons give practical guidance on surveillance and investigation of disease outbreaks and planning/implementation of appropriate health interventions.
• At the end of this lesson, you must be able to describe concepts and principals of demography in public health.
• You should also be able to analyze the vital statistics as health indicators and enumerate the epidemiologic models of disease causation.

Definition of Terms: Demography

• Demography is the statistical study of human populations which examines the size, structure, and movements of populations over space and time.
• Governments and private businesses use demography to analyze and predict social, cultural, and economic trends related to population.

Definition of Terms: Population Size

• Population size refers to the number of people in a given place or area at a given time.

Definition of Terms: Population Composition

• Population composition is when a population is characterized by certain variables like age, sex, occupation, or educational level.

Definition of Terms: Spatial Distribution

• Spatial distribution refers to how people are distributed in a specific geographic location.

Demography: Sources of Demographic Data

• There are two types of Demographic Data: Primary and Secondary.

Sources of Demographic Data: Primary data

• Primary data has not been gathered before.
• Nurses collect primary data through observation via surveys, informant interviews, community forums, and focus group discussions.

Sources of Demographic Data: Collecting Primary Data

• Primary Data is collected through Observation and Survey/Census.
• Observation is collection through ocular/windshield survey and participant observation.
• Survey/Census is the official periodic enumeration of population, in which demographic, economic, and social data are collected from specified population groups.
• There are two ways of assigning people during the census: De jure and De facto.
• De jure is when people are assigned to the place where they usually live regardless of where they are at the time of the census.
• De facto is when people are assigned to the place where they are physically present at the time of the census regardless of their usual place of residence.
• Informant interviews are purposeful talks with either key informants or ordinary members of the community.
• Key informants are formal and informal community leaders or persons of position and influence like leaders in local government, schools, and business.
• A community forum is an open meeting of the members of the community,
• A Focus group differs from a community forum - it is a much smaller group, usually 6-12 members only.
• For example, a focus group of first-time pregnant women.

Sources of Demographic Data: Secondary data

• Secondary data are taken from existing data sources.
• Sources consist of vital registries, health records and reports, disease registries, and census data

Sources of Demographic Data: Collecting Secondary Data

• Secondary Data is collected through Vital Events Registry, Health Records and reports and Disease registries.
• A Vital Events Registry is responsible for office and field work primarily involving the collection, processing, and dissemination of medical and demographic data obtained from vital statistics documents such as births, deaths, fetal deaths, marriages and divorces.
• Health Records and reports systematically evaluate patient progress and treatment outcomes, as well as to monitor overall program performance through Field Health Services Information System (FHSIS).
• Field Health Services Information System (FHSIS) is a network information source developed by the Department of Health (DOH) to enable it to better manage in nationwide health services delivery activities.
• It helps the local government determine public health priorities and is a basis for monitoring and evaluation of health program implementation and a basis for planning, budgeting, logistics and unusual occurrence of a disease.
• Census Data is a source of demographic information.

Demographic Indicators

• These include Population Size, Population Composition, and Population Distribution.

Demographic Indicators: Population Size

• Population size is the number of individuals within a population: Population size is defined as the number of individuals present in a subjectively designated geographic range.

Demographic Indicators: Methods of measuring the population size

• Methods of measuring the population size include: Determining the increase in the population resulting from excess of births compared to death and determining the increase in the population using data obtained during two census periods.
• Determining the increase in the population resulting from excess of births compared to death can be done in 2 ways using Natural Increase rate or the Rate of Natural Increase.

Demographic Indicators: Natural Increase

• Natural increase is simply the difference between the number of births and the number of deaths occurring in a population in a specified period of time.
• Natural Increase = Number of births - Number of deaths (specified year)
• Rate of Natural Increase is the difference between the Crude Birth Rate (CBR) and Crude Death Rate (CDR) occurring in a population in a specified period of time.
• Rate of Natural Increase = Crude Birth Rate - Crude Death Rate (specified year)

Demographic Indicators: Increase in population using two census periods:

• Determine the increase in the population using data obtained during two census periods, which implies that the increase in the size of the population is not merely attributed to excess in births but also the effect of migration.
• These are Absolute Increase per year and Relative increase.
• Absolute increase per year measures the number of people that are added to the population per year with the formula:
• Absolute increase per year = (Pt -Po)/t
  • Where: Pt = population size at a later time, Po = population size at an earlier time and t = number of years between time 0 and time t
• Relative increase is the actual difference between the two census counts expressed in the percent relative to the population size made during an earlier census with the formula:
• Relative increase = (Pt -Po)/Po
  • Where: Pt = population size at a later time and Po = population size at an earlier time

Demographic Indicators: Population Composition (Age and Sex)

• The composition of population is commonly described in terms of its age and sex.
• Nurses use age and sex composition data to decide which population groups merit attention in terms of health services and programs.
• Sex Composition is used to describe the sex composition of the population.
• Nurses compute for the sex ratio (compares the number of males to the number of females in the population).
• Sex Ratio = (Number of males/Number of females) x 100
• The sex ratio represents the number of males for every 100 females in the population.
• Knowing the working population (mainly youths) helps determine the extent of medical facilities needed for the number of aged population.
• Two ways to describe the age composition of the population are using the median age and dependency ratio.
• Median Age: divides the population into two equal parts.
• If the median age is said to be 19 years old, half of the population belongs to 19 years and above, while the other half belongs to ages below 19 years old.
• Dependency Ratio compares the number of economically dependent with the economically productive group in the population.
• The economically dependent are those who belong to the 0-14 and 65 and above age groups.
• Those considered to be economically productive are those within the 15 to 64 age group.
• Dependency Ratio = (Total population of the 0-14 and 65 and above age group)/ (Total population of 15-64 age group) x 100
• The dependency ratio represents the number of economically dependent for every 100 economically productive

Demographic Indicators: Age and Sex Composition

• Age and sex composition can also be described at the same time using a Population Pyramid which is a graphical representation of the age and sex composition of the population.
• Steps to construct the pyramid: compute the percentage of the population falling in each age-sex group using the total population as the denominator, each age group is represented by a horizontal bar where the first bar represents the youngest age group and drawn at the base of the pyramid.
• The bars for males are presented on the left side of the central vertical axis while bars for females are on the right side. The length of each bar corresponds to the % of the population falling in the specific age and sex group being plotted.

Demographic Indicators: Population Distribution

• Population distribution in space can be described in terms of urban-rural distribution, population density, and crowding index.
• Urban-rural distribution: illustrates the proportion of the people living in urban compared to the rural areas.
• Crowding Index: is described by dividing the number of persons in a household with the number of rooms used by the family for sleeping.
• Crowding Index = (Number of persons in a household)/(Number of rooms used for sleeping)
• Population Density = determines how congested a place is and provides implications in terms of the adequacy of basic health services present in the community.
• Population Density = (Number of people)/(Land area in terms of square meter or kilometer)

Vital Statistics: Definition of terms

• Vital Statistics: refers to the systematic study of vital events such as births, illnesses, marriages, divorce, separation and deaths.
• Vital Statistics: Rate shows the relationship between a vital event and those persons exposed to the occurrence of said event, within a given area and during a specified unit of time, it is evident that the person experiencing the event (Numerator) must come from the total population exposed to the risk of same event (Denominator).
• Vital Statistics: Ratio is used to describe the relationship between two (2) numerical quantities or measure of events without taking particular considerations to the time and place. These quantities need not necessarily represent the same entities, although the unit measure must be the same for both numerator and denominator of the ration.
• Vital Statistics: Crude (or General) Rate - referred to the total living population which indicates that the total population was exposed to the risk of the occurrence of the event.
• Vital Statistics: Specific Rate - the relationship is for a specific population class or group which limits the occurrence of the event to the portion of the population definitely exposed to it.
• Vital Statistics: Crude Birth Rate - a measure of one characteristic of the natural growth or increase of a population.

Vital Statistics: Purpose of Vital Statistics

• Vital statistics serve as indices of the health and illness statues of a community and serves as bases for planning, implementing, monitoring and evaluating community health nursing programs and services.
• Relevant data includes population census, registration of vital data, health Survey, and studies and researches.

Vital Health Indicators: Population indicators: Fertility Rates

• Includes Crude Birth Rate and General Fertility Rate.
• Crude Birth Rate: a measure of one of the characteristics of natural growth or increase in population. (Number of live births/Midyear population) x 1000
• General Fertility Rate is the number of livebirth per 1,000 women aged 15-49 in a given year. (Number of live births/Midyear population of women, 15-49 years of age) x 1000

Vital Health Indicators: Morbidity indicators

• Include Incidence Rate and Prevalence Rate.
• Incidence Rate measures the frequency of occurrence of the phenomenon during a given period of time and deals only with new cases: (Number of new cases of disease developing from a period of time/Population at risk of developing the disease) x F
• Prevalence Rate measures the portion of the population which exhibits a particular disease at a particular time, which can only be determined following a survey of the population concerned, and deals with total (old and new) number of cases. (Number of old and new cases of a disease/Population examined) x F
• Attack Rate is used when the risk period for the occurrence of disease is very short. (Number of new cases among the population during the period/Population at risk at the beginning of period) x 100

Vital Health Indicators: Mortality indicators

Include Crude Death Rate, Specific Mortality Rate, Cause-of-Death Rate, Infant Mortality Rate, Neonatal Mortality Rate, and Maternal Mortality Rate:

• Crude Death Rate is a measure of one mortality from all causes which may result in a decrease in population. (Number of deaths/Midyear Population) x 1000
• Specific Mortality Rate shows rates of dying in a specific population group. (Number of deaths in a specified group in a calendar year/Midyear population of the same specified group) x 1000
• Cause-of-Death Rate is the rate of dying due to a specific cause. (Number of deaths in a certain cause in a calendar year/Midyear population) x 1000
• Infant Mortality Rate measures the risk of dying during the first year of life, and is a good index of the general health condition of community since it reflects the changes in the environmental and medical conditions of the community. (Deaths under one year of age/Number of live births) x 1000
• Neonatal Mortality Rate measures the risk of dying on the first month of life, and may serve as index of the effects of prenatal care and obstetrical management of the newborn. (Number of deaths below 28 days/Number of live births) x 1000
• Maternal Mortality Rate measures the risk of dying from causes related to pregnancy, childbirth and puerperium, and is an index of obstetrical care needed and received by the women in a community. (Number of deaths due to pregnancy, delivery and puerperium/Number of live births) x 1000

Vital Health Indicators: Proportionate Mortality Rate, Swaroops Index and Case Fatality Rate

• Proportionate Mortality rate shows the numerical relationship between death from a cause (or group of cause), age (or groups of age) etc. and the total number of deaths from all causes in all ages taken together but is not a measurement of risk of dying. (Number of deaths from a particular cause/Total deaths) x 100
• Swaroop's Index measures the deaths among individuals in the age group of 50 and above, where the higher the rate, the better is the health status of the population. (Number of deaths among those 50 years and over/Total deaths) x 100
• Case Fatality Rate is an index of the killing power of a disease, and is influenced by incomplete reporting and poor morbidity data. (Number of deaths from a specified cause/Number of cases of the same disease) x 100

Presentation of Data

• Data is presented in forms of tables, charts, and graphs and the following are most commonly used graphs; line or curved graphs, bar graphs and area Diagrams:
• Line or curved graphs shows peaks, valleys, and seasonal trends and are used to show the trends of birth and death rates over a period of time.
• Bar graphs each bar represents or expresses a quantity in terms of rates or percentages of a particular observation like cause of illness and deaths.
• Area Diagram shows the relative importance of parts to the whole.

Definition of Terms: Epidemiology

• Epidemiology examines occurrence and distribution of health such as disease, death, deformities or disabilities on human population, and is concerned with identifying probable factors that influence the development of those conditions.
• Epidemiology is also used to analyze the different factors that contribute to disease development.

Definition of Terms: Agent and Host

• Agent is an inanimate or living organism that cause disease, they may be biologic, chemical, physical, mechanical or nutritive, agent characteristics can be described in terms of virulence, toxicity, intensity, impact or deficiency/excess.
• Host is any organism that harbors and provides nourishment for another organism where Host characteristics can be described in terms of their susceptibility or resistance against effects of a particular agent and may be influenced by the demographic and biologic factors along with personal habits.
• Specific resistance is immunologic experience while non-specific resistance results from intact skin and mucous membrane, good hygiene, reflexes like coughing.
• Herd immunity represents the immunity and susceptibility levels of individuals comprising the population.
• Environment includes the sum total of all external conditions and influences that affects life and development of an individual organism.
• The environment refers to the physical, biologic and sociological environments.

Practical Applications and Functions Related to Epidemiology

• Practical applications of epidemiology include assessment of the health status of the community or community diagnosis, the elucidation of the natural history of disease, determination of disease causation, prevention and control disease, monitoring and evaluation of health interventions and provision of evidence for policy formulation.
• Functions of the Epidemiology Nurse include implementation of public health surveillance, monitoring local health personnel conducting disease surveillance, conducting and/or assist other health personnel in outbreak investigation, assistance in the conduct of rapid surveys and surveillance during disasters.
• Further, assist in the conduct of surveys, program evaluations, and other epidemiologic studies, assist in the conduct of training courses in epidemiology, assist the epidemiologist in preparing the annual report and financial plan, and being responsible for inventory and maintenance of epidemiology and surveillance unit equipment.

Concepts and Principles of Epidemiology: Multiple Causation Theory or the Ecologic Concept of Disease

• Disease results from an imbalance between the disease agent and man as the host where the nature and extent of imbalance depends upon nature and characteristics of agent and host.
• The characteristics of agent and host and their interactions are directly related to and largely dependent on the nature of the environment.

Concepts and Principles of Epidemiology: Models

• There are 3 models that explain the Multiple Causation Theory: Wheel, Web, and Ecological Triad models.
• The Wheel Model gives emphasis on the role of the genetic make-up of the host (inner core), where the middle core represents the host's characteristics like sex, age and behaviors and the outer core represents the biologic, physical, and social environment.
• The Web Model depicts the intricate interrelationships of the various socio-demographic characteristics and behaviors of the host as well as the numerous environmental factors.
• The Ecological Triad is developed to further the understanding of the dynamic interrelations among various personal and environmental factors.

The Epidemiological Triangle

• The Epidemiologic Triangle consists of three components: Host, Agent and Environment.
• Three components of environment: Physical environment, Biological environment, Socio-economic environment.
• Physical environment is composed of the inanimate surrounding such as the geophysical condition of the climate.
• Biological environment makes up the living things around us such as plants and animal life.
• Socio-economic environment which may be in the form of level of economic development of the community, presence of social disruptions and the like.
• The model implies that each must be analyzed and understood for comprehensions and prediction of patterns of a disease, and that a change in any component will alter an existing equilibrium to increase or decrease the frequency of the disease.

Natural Life History of Disease

• Describing the natural history of disease seeks to identify factors related to the course of a disease once established to determine its duration and the probability of the various possible outcomes such as recovery, death or specific complications.
• Stages in the Natural Life History of Disease: Pre-pathogenesis or susceptibility and Pathogenesis
• Pre-pathogenesis or susceptibility stage is when disease has not developed but factors that favor its occurrence are present
• Pathogenesis stage is when a disease has developed and includes three substages: Pre-symptomatic disease or early pathogenesis, discernible lesion, and advanced disease
• Pre-symptomatic disease or early pathogenesis is when an individual has no symptoms that indicate presence of illness but in fact, pathogenic changes has begun.
• Discernible lesion is when changes may be detectable through sophisticated laboratory tests while early signs and symptoms of disease are developing.
• Advanced disease is when anatomical or functional changes have produced recognizable signs and symptoms.

Levels of Disease Prevention

• There is Primary, Secondary, and Tertiary prevention.
• Primary Prevention includes efforts to control the underlying cause or condition that results in disability.
• Secondary Prevention aims at preventing and existing illness or injury from progressing to long-term disability.
• The stages of application of such prevention include: i. Pre-pathogenesis, ii. Pathogenesis includes Early pathogenesis and discernible Lesion, and Advanced Disease.

Disease Prevention and Specific Interventions

• Primary prevention focuses on interrelations of various host agent and environmental factors to prevent development of disease.
• Interventions include health promotions with health education, nutrition counseling, personal hygiene, environmental sanitation, family planning and dental hygiene as well as specific protection through immunization, chemoprophylaxis, and protection against injuries and occupational hazards.
• Secondary Prevention Early focuses on interaction of host and stimulus to diagnose and treat disease and prevent to spread and further complications through early diagnosis and prompt treatment with screening, case-finding and selective examination.
• Tertiary prevention focuses on arrest of the disease process and prevention of further complications through arrest of the disease.
  • Disability Limiting interventions include rehabilitation and refraining for maximum use of remaining capacities.

Concepts of Causality & Association

• Disease does not occur at random and includes factors for preventing disease to occur or improve the overall quality of life: primary prevention for the well population to prevent health issues as well as secondary and tertiary prevention.
• Cause of a Disease is any event, condition, characteristics or a combination of these factors that play important role in producing the disease. Necessary cause refers to the fact that the factor must be present for the disease to occur.
• Sufficient cause indicates that if a factor is present, the disease can occur, but the factor's presence does not always result in the disease's occurrence.
• Risk is the probability of an unfavorable event such as disease, disability, defect or even death.
• Association states that if there is a concurrence of two variables more often than would be expected by chance, then the two variables are said to be associated, but does not necessarily imply a causal relationship.
• Factors associated with increased risk of a disease: predisposing, enabling and reinforcing
• Predisposing factors are any characteristics of an individual, a community or an environment that predisposes behavior or other conditions related to health, includes knowledge, belief and attitude but may include factors such as socio-economic status.
• Enabling factors are any characteristic of an individual, group or the environment that facilitates or make possible a certain health behavior or other conditions affecting health, and includes any skill or resource required to attain that condition.
• Reinforcing factors are any reward or punishment or any feedback following or anticipated as a consequence of health behavior.

Association Types

• Spurious or artifactual association is the association when none actually exists.
• Indirect association is the presence of a known or unknown factor common to both a characteristic and a disease may wholly or partly explain a statistical association.
• Direct or causal association is the presence of a factor with wholly and directly explain the cause of disease with no intervening variables.
• One-to-one causal suggests that when one factor is present, disease results while conversely, when the disease is present, the factor must also be present.
• Multifactorial causation indicates several factors acting independently or synergistically can produce a disease.

Epidemiology Investigation/Approaches

• These include types of Epidemiological Approach and Analytical Epidemiology.

Types of Epidemiological Approach

• Descriptive epidemiology is concerned with describing the frequency and distribution of disease in a given population, where the nurse characterizes the disease episode by describing the characteristics of the person affected with the disease and pattern of disease onset in terms of time and place.
• Descriptive Epidemiology begins with observation and recording of existing patterns of occurrence of disease conditions through screening and case-finding, where:
• Screening is the presumptive identification of unrecognized diseases or defects through the application of diagnostic tests or laboratory examinations and clinical assessment that can be applied rapidly and inexpensively, with the primary goal being to detect a disease in its early stages.
• Case finding is done to look for previously unidentified cases of diseases.
• Sensitivity is the proportion of persons with a disease who test positive on a screening test; it measures the probability of the test correctly identifying a positive case of a disease (true-positive). (Describing disease as to person, place, and time characteristics.
• Specificity is the proportion of persons without a disease who have negative results on a screening test, it measures the probability of correctly identifying non-cases (true-negative).
• Describing the disease relating to the person, place and time characteristics, After the disease or condition has been identified with reasonable certainty, the number of persons who possess the disease are recorded noting down the characteristics of the afflicted persons, the time the disease was initially recognized and the characteristics of the place where the cases came from.
• The nurse determines the community's susceptibility as a host in terms of herd immunity, which is the state of resistance of a population group to a particular disease at a given time. In viewing
• Patterns of Occurrence and Distribution should also be considered, with the variables of disease as to person, time and place are reflected in distinct patterns of occurrence and distribution in a given community.
• The characteristics of such disease is sporadic which includes the intermittent occurrence of a few isolated and unrelated cases in a given locality. The cases are few and scattered, so that there is no apparent relationship between them and they occur on and off, intermittently, through a period of time.
• Disease is endemic when it shows continuous occurrence throughout a period of time such as that it is always occurring in the locality and the level of occurrence is more or less constant through a period of time. The level occurrence maybe low or high, when the given level is continuously maintained, then the pattern maybe low endemic or high endemic as the case maybe.
• The existence of Epidemic indicates a situation when there is a marked upward fluctuation in disease incidence
• Disease is pandemic when it is the simultaneous occurrence of epidemic of the same disease in several countries.
• Exposure or contact rate refers to opportunities for progressive transfer of an agent to a new host with possibility of contact between the source of infection and susceptible individual.
• The nurse attempts to correlate the data and attempts to formulate a causal association between the disease under study and the probable factors surrounding it with Analysis of the general pattern of occurrence of the disease or condition.

Analytical Epidemiology

• Attempts to analyze the causes or determinants of disease through hypothesis testing. It consists of hypothesis-testing of causal association using different epidemiological study designs, such as employing case-control and cohort studies/follow-up/incidence studies in investigating patterns of disease and cause in individuals and correlation or ecologic studies in analyzing patterns of disease and cause in population.
• Interventional or experimental Epidemiology aims to test effectiveness or reasonableness of intervention programs designed to prevent and control diseases utilizing randomized controlled or clinical trials, field or community trials.
• Evaluation Epidemiology attempts to measure the effectiveness of different health services and intervention programs.