Introduction to Public Health Practice
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Get Help Now!Concept of Health & Disease
Bachelor of Public Health
Faculty Name : Dr . Haresh
Date:9th November
Subject Code: BMPH01
Module No. 2 – Health from an ecological perspective
School of Public Health
1
Objective
2
At the end of this module, the students should be able to
Discuss the concept of health, illness and disease
Define Health
Describe how to measure health status
Learning Outcome
3
The students will gain the knowledge and understanding about the concept of health, disease and illness and will be able to apply this knowledge in solving the health problems of the community at large
Content
Concept of Health
Dimensions of Health
Spectrum of Health
Measurement of Health
4
Concept of Health
Biomedical concept
Ecological concept
Psychosocial concept
Holistic concept
5
Biomedical concept
Health is “absence of disease” ie if one is free from disease than he is considered healthy.
Based on germ theory of disease.
Question – malnutrition, chronic disease, accidents, drug abuse, mental illness , environmental pollution etc which lead to ecological concept
Ecological concept
Ecologists – health is dynamic equilibrium between man and his environment, and disease is maladjustment of the human organism to his environment.
“Health implies the relative absence of pain and discomfort and a continuous adaptation and adjustment to the environment to ensure optimal function”
Ecological concept
Raised two questions
Imperfect man
Imperfect environment
History shows that improvement in human adaptation to natural environment can lead to longer and better quality of life- even with the absence of modern health delivery services.
Psychosocial concept
Development in social science – Health is not only a biomedical phenomenon, but it is influenced by
social,
psychological,
cultural,
economic and
political factors of the people concerned,
“Health is both a biological and social phenomenon”
Holistic concept
It recognizes the strength of social, economic, political and environmental influences on health
Then came a many definitions of health
http://www.evolvehealth.nl/wp/wp-content/uploads/2012/07/IPS-Model.bmp
Synthesis of all the above
concepts,
Definitions of Health
“the condition of being sound in body, mind or spirit, especially freedom from physical disease or pain” (webster)
“soundness of body or mind; that condition in which its functions are duly and efficiently discharged” ( oxford)
“ a condition or quality of the human organism expressing the adequate functioning of the organism in given conditions, genetic and environmental” ( operational def by WHO)
Health Definition
WHO define health
“Health is a state of complete physical, mental and social well-being and not merely an absence of disease or infirmity”
The WHO definition of health emphasizes that there are different, complexly related forms of wellness and illness, and suggests that wide range of factors can influence the health of individuals and groups.
Health is not an absolute.
Health and disease are not necessarily opposites
Dimension of Health
Health is Multidimensional.
WHO definition envisages
Physical
dimension
Mental
Dimension
Social
Dimension
Physical dimension
The state of physical health implies the notion of “perfect functioning” of the body. It conceptualizes health biologically as a state in which every cell and every organ is functioning at optimum capacity and in perfect harmony with the rest of the body.
http://images01.trafficz.com/cache/h3w4/500_1189535325_running.jpg
Mental Dimension
Mental health is not mere absence of mental illness.
Good mental health is ability to respond to the many varied experience of life with flexibility and sense of purpose.
“A state of balance between the individual and the surrounding world, a state of harmony between oneself and others, a coexistence between the realities of the self and that of other people and that of the environment”
http://cms.mumbaimirror.com/portalfiles/7/3/200710/Image/Mental%20Health.jpg
Social dimension
Social well-being implies harmony and integration within the individual, between each individual and other members of society and between individuals and the world in which they live.
“quantity and quality of an individual’s interpersonal ties and the extent of involvement with the community.”
Concept of Illness
Subjective sense of feeling unwell that often motivates a patient to consult a physician.
Illness includes physical, psychological and social dimensions
Difficult to confirm by diagnostics tests
Concept of Disease
Disease and injury are viewed as phenomena that leads to significant loss or disability in social functioning, making one unable to carry out one’s main personal or social functions in life.
health is equivalent to the absence of disability; individuals able to carry out their basic functions in life are healthy.
Spectrum of Health
Health and disease lie along a continuum, and there is no single cut-off point.
Positive health
Better Health
Freedom from sickness
Unrecognized sickness
Mild sickness
Severe sickness
Death
The Health sickness spectrum
Spectrum concept of health
Emphasizes that the health of an individual is not static.
It is a dynamic phenomenon and a process of continuous change.
Measuring Health
Available information on health outcomes suggests that measuring health status of population is simple task.
But, commonly used measures of health status fail to paint a complete picture of health.
The commonly used measures reflect the disease and mortality, rather than health.
Mortality is used as proxy for health despite the problems
It is widely used to describe the health status of population.
Mortality data indirectly describe health status of living population.
Sources of morbidity data
Sources of information on morbidities and disabilities
include medical records, managed care organizations, and other providers.
Information derived from surveys, businesses, schools and other sources.
Eg: Health, United States, published by CDC
Mortality –based measures
Crude mortality rates
Age-specific
Age adjusted mortality
Life expectancy
Years of potential life lost(YPLL)
Crude Mortality Rate
Counts deaths within the entire population
Not sensitive to differences in the age distribution of different populations.
Limitation of Crude mortality rate:
Sources: http://www.cdc.gov/nchs/data/hestat/finaldeaths03/finaldeaths03_figure-1.png
From the figure above, we might conclude that mortality rates in United States had declined since 1960.
However because there was a greater proportion of late 20th century population in the higher age categories.
Therefore these are not truly comparable populations.
Age-Specific Mortality rates
Relates the number of deaths to the number of persons in a specific age group.
Eg: Infant mortality rate (IMR)
IMR- is the number of deaths of live-born infants occurring in the first year of life per 1000 live births.
Age-adjusted mortality rates
Public health studies use age-adjusted mortality rates to compensate for different mixes of age groups within a population.
Age-adjusted rates are calculated by applying age specific rates to a standard population.
This adjustment permits more meaningful comparisons of mortality experience between populations with different age distribution
Life Expectancy
Based on the mortality experience of a population, is a computation of the number of years between any given age (e.g., birth or age of 65 years) and the average age of death for that population.
Often used as comparison of health status among nations along with IMR.
Years of Potential Life Lost
Mortality based indicator that places greater weight on deaths that occur at younger age.
Arbitrary age( 65 to 75 years) are computed and used to measure the relative impact on society of different cause of death.
Example: If 65 years used as the threshold or calculating YPLL, an infant death would contribute 65 YPLL. And homicide at age 25 would contribute 40 YPLL
Morbidity, Disability and Quality Measures
These indicators are meaningful measure of health status in population as they consider morbidity and disabilty from conditions that impart on functioning not only cause death. ( eg: cerebral palsy, schizophrenia.)
Commonly used are Disability adjusted life years, span of healthy life indicator.
Summary
Contemporary philosophy of health has been quite focused on the problem of determining the nature of the concepts of health, illness and disease from a scientific point of view.
Some theorists claim and argue that these concepts are value-free and descriptive in the same sense as the concepts of atom, metal and rain are value-free and descriptive.
To say that a person has a certain disease or that he or she is unhealthy is thus to objectively describe this person.
On the other hand it certainly does not preclude an additional evaluation of the state of affairs as undesirable or bad. The basic scientific description and the evaluation are, however, two independent matters, according to this kind of theory
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References
Principles of Public Health Practice, 3rd Edition, F. Douglas
Developing Practice for Public Health and Health Promotion E-Book, 3rd Edition, Naidoo & Wills
Park’s Textbook of Preventive and Social Medicine, 20th Edition, K. Park
Community Medicine with Recent Advances, 3rd Edition, AH Suryakantha
phprimer.afmc.ca/…TheoryThinkingAboutHealth/Chapter1ConceptsOfH.
www.fil.lu.se/hommageawlodek/site/papper/NordenfeltLennart.pdf
https://pglibrary-publichealth.wikispaces.com/…/Concept+of+health+and…
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Introduction to Public Health Practice
Prevention Health Services
Program Name
Faculty Name :
Date:
Subject Code:
Module No. 4 – Public Health & Health Systems
School of Public Health
1
Objective
2
At the end of this module, the students should be able to
Describe the health system as a public health concern
Discuss Natural history of disease
Identify and describe the levels of prevention and modes of intervention
Learning Outcome
3
The students will acquire knowledge about the natural history of disease as well as the modes of intervention and will be able to apply this knowledge for the prevention of health problems in the community
Content
Public health system
Natural History of Disease
Levels of prevention
Modes of intervention
Health services pyramid
4
Public health system
Relationship between public health and other health activities has never been clear.
Different views prevail among health professionals
Public health is part of the health system or the health system is part of public health?
Most components serve the same ends
The term health system refers to all aspects of the organization, financing and provision of programs and services for prevention and treatment of illness and injury.
The public health system is a component of this larger health system.
Public commonly perceives the health system to include only medical care and treatment aspects of the overall system.
However, public health activities are part of larger set of activities that focus on health, well-being, disease and illness.
Some questions to brainstorm
Does the countries have a rational strategy for investing its resources to maintain and improve people’s health?
Is the current strategy excessive in ways that inequitably limited access to and benefit from needed services?
Is the health system accountable to its end-users and ultimate payers for the quality and results of its services.
The issues of health,
Excess
access,
Accountability
and quality
Make the health system a public health concern
Prevention and Health service
Health and illness are dynamic state that are influenced by a wide variety of biological, environmental, behavioral, social and health services factors acting through an ecological model.
The complex interaction of these factors results in the occurrence or absence of disease or injury.
Which in turn contributes to the health status of individuals and populations.
Prevention and Health services
Before we go to prevention, its necessary to understand the Natural history of disease.
The nineteenth-century revolution in thinking brought about by Koch and Pasteur led to the recognition of distinct stages in the development of a disease.
If left untreated, a disease would evolve through a series of stages that characterize its natural history
But if an intervention is applied, the natural history is modified, producing a typical clinical course for the condition
Natural history of disease
General strategies to maintain health before developing health
Two general strategies that seek to maintain health by intervening prior to the development of disease or injury.
Health promotion
Specific protection
Both involve activities that alter the interaction of the various health-influencing factors in ways that contribute to either averting or altering the likelihood of occurrence of disease or injury.
Health promotion and Specific Protection
Health promotion activities attempt to modify human behaviors by increasing the ability to resist disease or injury- including factors, thereby reducing or neutralizing risks to health.
Examples of health promotion activities include interventions such as nutrition counseling, genetic counseling, family counseling, and the myriad activities that constitute health education
Health promotion and Specific Protection
Health promotion also properly includes
Provision of adequate housing
Employment
Recreational conditions
Community development activities
It is somewhat ironic that activities that focus on the state of health and that seek to maintain and promote health are not commonly perceived to be “health services.
Specific protection activities provide individuals with resistance to factors (such as microorganisms like viruses and bacteria) or modify environments to decrease potentially harmful interactions of health-influencing factors (such as toxic exposures in the workplace).
Examples of specific protection
Use of protective equipment for asbestos removal)
Immunizations
Occupational
Environmental engineering,
Regulatory controls
Activities to protect individuals from environmental carcinogens
Exposure to second-hand or side-stream smoke
Toxins
Early Case Finding and Prompt Treatment, Disability Limitation, and Rehabilitation
Early detection and prompt treatment reduce individual pain and suffering and are less costly to both the individual and society
Interventions to achieve early detection and prompt treatment include
Screening tests
Case-finding efforts
Periodic physical exams
Screening tests, Case-finding efforts and Periodic physical exams
Screening tests are increasingly available to detect illnesses before they become symptomatic.
Case-finding efforts for both infectious and noninfectious conditions are directed at populations at greater risk for the condition on the basis of criteria appropriate for that condition.
Periodic physical exams
Strategy targeting disease is disability limitation through effective and complete treatment.
Efforts largely aim to arrest or eradicate disease or to limit disability and prevent death.
The final intervention strategy focusing on disease—rehabilitation—is designed to return individuals who have experienced a condition to the maximum level of function consistent with their capacities
Link with Prevention
Prevention in relation to the stage of the disease or condition.
Preventive intervention strategies are considered
Primary
Secondary
Tertiary
Primary prevention
Here the goal is to protect healthy people from developing a disease or experiencing an injury in the first place through reducing risk factor levels.
For example:
education about good nutrition, the importance of regular exercise, and the dangers of tobacco, alcohol and other drugs
education and legislation about proper seatbelt and helmet use
regular exams and screening tests to monitor risk factors for illness
immunization against infectious disease
controlling potential hazards at home and in the workplace
Secondary Prevention
These interventions happen after an illness or serious risk factors have already been diagnosed. The goal is to halt or slow the progress of disease (if possible) in its earliest stages; in the case of injury, goals include limiting long-term disability and preventing re-injury.
For example:
telling people to take daily, low-dose aspirin to prevent a first or second heart attack or stroke
recommending regular exams and screening tests in people with known risk factors for illness
providing suitably modified work for injured workers
Tertiary prevention
This focuses on helping people manage complicated, long-term health problems such as diabetes, heart disease, cancer and chronic musculoskeletal pain. The goals include preventing further physical deterioration and maximizing quality of life.
For example:
cardiac or stroke rehabilitation programs
chronic pain management programs
patient support groups
Prevention strategies in relation to population disease status and effect on disease incidence and prevalence.
Primary prevention aims to reduce the incidence of conditions,
Secondary and tertiary prevention seek to reduce prevalence by shortening duration and minimizing the effects of disease or injury
Relationship of health promotion and specific protection to levels of prevention
Primary, secondary and tertiary
Relationship with Health promotion and specific protection are primary prevention strategies seeking to prevent the development of disease.
Early case finding and prompt treatment represent secondary prevention, because they seek to interrupt the disease process before it becomes symptomatic
Disability limitation and rehabilitation are considered tertiary-level prevention in that they seek to prevent or reduce disability associated with disease or injury.
Links with Public Health and Medical Practice
Its allocation of responsibilities for carrying out the various interventions.
Three practice domains can be roughly delineated:
Public health practice
Medical practice
Long-term care practice
Public health practice
Primary goal: health promotion, specific protection and early case finding.
The concept of public health practice here is a broad one that accommodates the activities carried out by many different types of health professionals and workers, not only those working in public health agencies
Public health practice occurs in voluntary health agencies, as well as in settings such as schools, social service agencies, industry, and even traditional medical care settings.
Health Care Pyramid Levels
Primary, Secondary and Tertiary medical care
Primary medical care
Focuses on the basic health needs of individual and families
First contact health care in the view of the patient
Provides 80% of necessary care, includes comprehensive array of services,
Onsite referral, health promotion and disease prevention
Curative services
Secondary care
Specialized care serving the major share of remain 20% of need beyond scope of primary care.
Physicians or hospitals provide secondary care , generally on referal from primacy care
Tertiary medical care
Highly specialized and technologically sophisticated medical and surgical care
For complex conditions
Provided in large medical centers or academic health centers.
Long-term care practices
Long-term care is appropriately classified separately because of the special needs of the population requiring such services and the specialized settings where many of these services are offered.
This, too, is changing as specialized long-term care services increasingly move out of long-term care facilities and into home settings.
Everyone should be served by population-wide public health services, and nearly everyone should be served by primary medical care.
However, increasingly smaller proportions of the total population require secondary – and tertiary-level medical care services
Health services pyramid
Primary prevention
Secondary prevention
Tertiary prevention
Tertiary health care
Secondary health care
Primary health care
Population-based public health services
Public Health and Medical Practice Interfaces
Public health and medical practice are presented as separate domains of practice, there are many interfaces that provide a template for either collaboration or conflict.
Public health practitioners have traditionally deferred to medical practitioners for providing the broad spectrum of services for disease and injuries in individuals
Medical practitioners have generally acknowledged the need for public health practice for health promotion and specific protection strategies
Summary
Generally, primary preventive services are community-based and are targeted toward populations or groups rather than individuals.
Early case-finding activities can be directed toward groups or toward individuals
Long-term care involves elements of both community-based service and individually oriented service.
33
References
Principles of Public Health Practice, 3rd Edition, F. Douglas
Developing Practice for Public Health and Health Promotion E-Book, 3rd Edition, Naidoo & Wills
Park’s Textbook of Preventive and Social Medicine, 20th Edition, K. Park
Community Medicine with Recent Advances, 3rd Edition, AH Suryakantha
http://www.jblearning.com/samples/0763745251/45251_CH03_049_072.pdf
www.ashp.org/DocLibrary/Bookstore/P1725-Chapter9.aspx
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Module 7.2
SAMPLING TECHNIQUE
Learning objectives At the end of this session, students will be able to Explain use of sampling List the type of sampling methods Select appropriate sampling method
List of Topics
Definition and use of Sampling
Sampling methods
Sampling error
Definition of sampling Procedure by which some members of the population are
selected as representatives of the entire population Study population The study population is the population to which the results of the study will be inferred
The study population depends upon the research question How many injections do people receive each year in India? Study population: Population of India
How many needle-sticks to health care workers experience each year in India? Study population: Health care workers of India
How many hospitals have a needle-stick prevention policy in India? Study population: Hospitals of India
SAMPLE – Representative of time Seasonality Day of the week Time of the day SAMPLE – Representative of place Urban Rural SAMPLE – Representative of persons Age Sex Other demographic characteristics
TERMINOLOGY
Sampling unit (Basic Sampling Unit, BSU) Elementary unit that will be sampled People Health care workers Hospitals
Sampling frame List of all sampling units in the population
Sampling scheme Method used to select sampling units from the sampling
frame
WHY TO SAMPLE
Obtain information from large populations
Ensure the efficiency of a study
Obtain more accurate information
Population
Infinite/finite size Characterized by unknown
parameters
Sample
• Finite size • Characterized by
measurable parameters (e.g., mean, standard dev.)
A sample is a part of the population, selected by the investigator to gather information (measures) on certain characteristics of the original population
SAMPLING Non – probability Probability
Non-probability samples Probability of being selected is unknown Convenience samples Biased Best or worst scenario
Subjective samples Based on knowledge Time/resource constraints
Probability samples Every unit in the population has a known probability of being
selected Only sampling method that allows to draw valid conclusions
about population
Probability samples Removes the possibility of bias in selection of subjects Ensures that each subject has a known probability of being
chosen Allows application of statistical theory
Methods used in probability samples 1. Simple, random sampling 2. Systematic sampling 3. Stratified sampling 4. Cluster sampling 5. Multistage sampling
Simple, random sampling Principle Equal chance for each statistical unit
Procedure Number all units Randomly draw units
Advantages Simple Sampling error easily measured
Disadvantages Need complete list of units Does not always achieve best representatively
METHODS OF SRS Lottery method Random number table
EXAMPLE OF SRS 1 Albert D. 2 Richard D. 3 Belle H. 4 Raymond L. 5 Stéphane B. 6 Albert T. 7 Jean William V. 8 André D. 9 Denis C. 10 Anthony Q. 11 James B. 12 Denis G. 13 Amanda L. 14 Jennifer L. 15 Philippe K. 16 Eve F. 17 Priscilla O. 18 Frank V.L. 19 Brian F. 20 Hellène H. 21 Isabelle R. 22 Jean T. 23 Samanta D. 24 Berthe L.
25 Monique Q. 26 Régine D. 27 Lucille L. 28 Jérémy W. 29 Gilles D. 30 Renaud S. 31 Pierre K. 32 Mike R. 33 Marie M. 34 Gaétan Z. 35 Fidèle D. 36 Maria P. 37 Anne-Marie G. 38 Michel K. 39 Gaston C. 40 Alain M. 41 Olivier P. 42 Geneviève M. 43 Berthe D. 44 Jean Pierre P. 45 Jacques B. 46 François P. 47 Dominique M. 48 Antoine C.
Systematic sampling Principle A unit drawn every k units Equal chance of being drawn for each unit
Procedure Calculate sampling fraction/interval (k = N/n) Draw a random number (≤ k) for starting Draw every k units from first unit
Advantages Ensures representatively across list Easy to implement
Disadvantage Dangerous if list has cycles
Example of systematic random
Stratified sampling Principle Classify population into homogeneous subgroups (strata) Draw sample in each strata Combine results of all strata
Advantage More precise if variable associated with strata All subgroups represented, allowing separate conclusions
about each of them Disadvantages Sampling error difficult to measure Loss of precision if small numbers sampled in individual
strata
Cluster sampling
Principle Random sample of groups (“clusters”) of
units All or proportion of units included in selected
clusters Advantages Simple: No list of units required Less travel/resources required
Disadvantages Imprecise if clusters homogeneous (Large
design effect) Sampling error difficult to measure
Cluster sampling The sampling unit is not a subject, but a group (cluster) of
subjects. It is assumed that: The variability among clusters is minimal The variability within each cluster is what is observed in the
general population
The two stages of a cluster sample
1. First stage: Probability proportional to size • Select the number of clusters to be included • Compute a cumulative list of the populations in each unit
with a grand total • Divide the grand total by the number of clusters and obtain
the sampling interval • Choose a random number and identify the first cluster • Add the sampling interval and identify the second cluster • By repeating the same procedure, identify all the clusters
The two stages of a cluster sample 2. Second stage
• In each cluster select a random sample using a sampling frame of subjects (e.g. residents) or households
Self-weighting in cluster samples Stage one: The larger units are more likely to be
selected in the first round Unit B twice as large as unit A, hence unit B will have twice
the chance of being selected Stage two: Individuals in larger unit selected are less
likely to be selected in the second round Individual in unit B will have half the chance of being
selected within the unit The two effects cancel each other and each person in
the population has the same probability of being sampled
WHO – 30 x 7 cluster sampling Procedure: list of all villages (areas) with total population
Village Inhabitants Cumulative 1 34 34 2 60 94 3 30 124 4 76 200 5 315 515
4,715
Divide the cumulative total by 30 clusters we wish to select
4,715 : 30= 157.1
Find a random number with three digits (= Sampling interval) e.g. 123
Choose from the cumulative distribution the clusters by adding 157 (sampling interval)
3 124 124 * 1st cluster 4 76 200 5 315 515 ** 2nd
123+157=280
In each village (area) choose 7 children, randomly
Total sample 30 X 7= 210
Example of cluster sampling
Village 4
Village 5
Village 3
Village 2Village 1
Multistage sampling Principle Several chained samples Several statistical units
Advantages No complete listing of population required Most feasible approach for large populations
Disadvantages Several sampling lists Sampling error difficult to measure
Non-probability samples Probability of being selected is unknown Convenience samples Biased Best or worst scenario
Subjective samples Based on knowledge Time/resource constraints
Purposive sampling, Quota sampling
Sampling errors We observe a sample instead of the whole population. If we take repeated samples from the same population, the
results obtained from one sample differ from the results of another sample.
This type of variation is called sampling error.
Sampling error No sample is a perfect mirror image of the population Magnitude of error can be measured in probability samples Expressed by standard error of mean, proportion, differences… Function of: Sample size Variability in measurement
References
• Sandelowski, M. (1995). Sample size in qualitative
research. Research in Nursing & Health, 18, 179–183.
• Emmel, N. (2013). Sampling and choosing cases in qualitative
research:A realist approach. London: Sage.
• NIST/SEMATECH, “7.2.4.2. Sample sizes required”, e-Handbook
of Statistical Methods.
• Kish, L. (1965). Survey Sampling.Wiley. ISBN 0-471-48900-X.
- Module 7.2��SAMPLING TECHNIQUE
- Learning objectives
- List of Topics
- Definition of sampling
- The study population depends upon the research question
- Slide Number 6
- TERMINOLOGY
- WHY TO SAMPLE
- Population
- SAMPLING
- Non-probability samples
- Probability samples
- Probability samples
- Methods used in probability samples
- Simple, random sampling
- METHODS OF SRS
- EXAMPLE OF SRS
- Systematic sampling
- Example of systematic random
- Stratified sampling
- Cluster sampling
- Cluster sampling
- The two stages of a cluster sample
- The two stages of a cluster sample
- Self-weighting in cluster samples
- WHO – 30 x 7 cluster sampling
- Slide Number 27
- Slide Number 28
- Multistage sampling
- Non-probability samples
- Sampling errors
- Sampling error
- Slide Number 33
- Slide Number 34
Module 7.1
Sampling
SAMPLE SIZE DETERMINATION
Learning Objectives
At the end of this module, the students will be able to describe :
sampling and its purpose.
need of Sample size in research .
List of Topics
Purpose of sampling
Sampling in Descriptive survey
Sample size determination
Adequacy of sample size
WHAT IS THE PURPOSE OF SAMPLING?
The purpose of sampling is to examine some portion of the population and
To extend the knowledge obtained from the sample to the population at large.
RELATIONSHIP BETWEEN POPULATION AND SAMPLE
PLACE OF SAMPLING IN DESCRIPTIVE SURVEYS Define objectives
Identify study population
Establish Plan of Analysis
Identify variables to study
Choose sampling frame
PLACE OF SAMPLING IN DESCRIPTIVE SURVEYS CONT… Select sample
Design questionnaire
Collect data
Analyse data
Communicate results
Use results
SAMPLE SIZE DETERMINATION
No universal answer
Assumption dependent (and therefore partly subjective)
Other considerations (cost, time-frame, feasibility)
NEED FOR ADEQUATE SAMPLE SIZE Studies on small number of subjects
– May fail to detect important effects – May estimate effects imprecisely
Studies on larger number of subjects – Waste of resources – May lead to a loss in accuracy
ADEQUACY OF SAMPLE SIZE Depends on the scope of the study
Curative effect of a drug for AIDS
– Single positive result is important
– Sample size may be irrelevant
ADEQUACY OF SAMPLE SIZE CONT … Testing new malaria vaccine
– Several known preventive measures of varying effectiveness
– Vaccine should be tested on adequate number of subjects
TYPES OF OUTCOME MEASURES
Proportion, Mean
• Proportion of subjects who develop
malaria after entering high risk area.
• Mean Cholesterol level among the
diabetic individuals
HOW LARGE A SAMPLE DO I NEED?
Depends on the aim(s) of the study
Reasonable guess of the expected result
How precise the result should be?
Operational constraints
Relevant information
SELECTION OF SAMPLE SIZE
1) If we take the small samples < 30 % our study is not valid
2) If we take large samples > 75 % it is laborious to do
3) We need optimum size which gives reliable results minimum sample size advised is 30 %
80%
20%
25%
70%
30%
75%
HOW TO FIND SUITABLE SAMPLE SIZE
151 June 2016
DataQualitative Quantitative
Find Permissible or Allowable error L
Error Not Exceed 10% Or 20 %
Error Not Exceed 1 % Or 2 %
Find 30 % Incidence or Prevalence
10 % L = 30 / 100 * 10 = 3
20 % L = 30 / 100 * 20 = 6
1 % L = 30 / 100 * 1 = 0.3
2 % L = 30 / 100 * 2 = 0.6
n = 4 * p * q / L 2 n = 4 σ 2 / L 2
10 % n = 4 * 30 * 70 / 3 * 3 = 933
20 % n = 4 * 30 * 70 / 6 * 6 = 233
1 % n = 4 * 8 * 8 / 0.3 * 0.3 = 2844
2 % n = 4 * 8 * 8 / 0.6 * 0.6 = 711
References Sandelowski, M. (1995). Sample size in qualitative
research. Research in Nursing & Health, 18, 179–183.
Emmel, N. (2013). Sampling and choosing cases in qualitative
research: A realist approach. London: Sage.
References
NIST/SEMATECH, “7.2.4.2. Sample sizes required”, e-
Handbook of Statistical Methods.
Kish, L. (1965). Survey Sampling. Wiley. ISBN 0-471-48900-X
Epidemiology workshop series Community Medicine
- Module 7.1��Sampling
- Learning Objectives
- List of Topics
- WHAT IS THE PURPOSE OF SAMPLING?
- RELATIONSHIP BETWEEN POPULATION AND SAMPLE
- PLACE OF SAMPLING IN DESCRIPTIVE SURVEYS
- PLACE OF SAMPLING IN DESCRIPTIVE SURVEYS CONT…
- SAMPLE SIZE DETERMINATION
- �NEED FOR ADEQUATE SAMPLE SIZE�
- ADEQUACY OF SAMPLE SIZE
- �ADEQUACY OF SAMPLE SIZE �CONT …�
- TYPES OF OUTCOME MEASURES
- �HOW LARGE A SAMPLE DO I NEED?�
- SELECTION OF SAMPLE SIZE
- HOW TO FIND SUITABLE SAMPLE SIZE
- References
- References
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