Zsuzsanna Elekes
Methods of epidemiology
Ez a tantárgyi prezentációs anyag az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósult meg, a TAMOP-4.1.2-
08/2/A/KMR-0043 "A szociálpolitikus és szociális munkás képzés megújítása az ELTE és a BCE együttműködésében (SZOCMEG)" projekt
keretében.
Definitions
Priciples of Epidemiology in Public Health Practice U.S.
Department of Health and Human Services p: 1-1 – 1-81 http://www.ihs.gov/medicalprograms/portlandinjury/pdfs/pr
inciplesofepidemiologyinpublichealthpractice.pdf
Epidemiology is the basic science of public health
• quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods.
• a method of causal reasoning based on developing
• a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors,
• Epidemiology provides the foundation for
directing practical and appropriate public health action based on this science and causal reasoning.
• Epidemiology is 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
study to the control of health problems
• The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of.
Uses:
• Assessing the community’s health
• Making individual decisions
• Completing the clinical picture
• Searching for causes
• Searching for causes
History
• 400 B - Hippocrates suggested that environmental and host factors such as behaviors might influence the development of disease.
• 1662- John Graunt: quantifys patterns of birth, death, and disease occurrence, noting disparities between males and females, high infant mortality, urban/rural differences, and seasonal variations urban/rural differences, and seasonal variations
• 1800- William Farr systematically collects and analyzes Britain’s mortality statistics
• 1854 – John Snow the ”father of epidemiology”
• Late 1800’s - investigators focused on acute infectious diseases.
• In the 1930s and 1940s, epidemiologists extended their methods to noninfectious diseases
• During the 1960s and early 1970s health workers applied epidemiologic methods to eradicate
naturally occurring smallpox worldwide naturally occurring smallpox worldwide
• Today, public health workers throughout the world accept and use epidemiology regularly to characterize the health of their communities and to solve day-to-day problems
Morbidity measures:
• Incidence proportion or risk:
– Incidence proportion is the proportion of an initially disease-free population that develops disease, becomes injured, or dies during a specified (usually limited)
period of time.
– Method of calculating incidence:
• Attack rate:
– The risk of getting the disease during a specified period, such as the duration of an outbreak. A variety of attack rates can be calculated.
• Prevalence
– Prevalence, sometimes referred to as
prevalence rate, is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.
– Point prevalence refers to the prevalence – Point prevalence refers to the prevalence
measured at a particular point in time.
– Period prevalence refers to prevalence measured over an interval of time.
– Method for calculating prevalence of disease
– Method for calculating prevalence of an attribute
attribute
Mortality rates
• Motality rate
– A mortality rate is a measure of the frequency of occurrence of death in a defined population during a specified interval.
• Crude mortality rate (crude death rate)
– The crude mortality rate is the mortality rate from all causes of death for a population.
• Cause-specific mortality rate
– The cause-specific mortality rate is the
mortality rate from a specified cause for a mortality rate from a specified cause for a population. The numerator is the number of deaths attributed to a specific cause. The
denominator remains the size of the population at the midpoint of the time period.
• Age-specific mortality rate
– An age-specific mortality rate is a mortality rate limited to a particular age group. The
numerator is the number of deaths in that age group; the denominator is the number of
persons in that age group in the population
• Infant mortality rate
• Infant mortality rate
– The infant mortality rate is perhaps the most commonly used measure for comparing health status among nations:
• Years of potential life lost (YPLL)
– Years of potential life lost (YPLL) is one
measure of the impact of premature mortality on a population. Additional measures
incorporate disability and other measures of quality of life. YPLL is calculated as the sum of the differences between a predetermined end the differences between a predetermined end point and the ages of death for those who died before that end point. The two most commonly used end points are age 65 years and average life expectancy.
Descriptive epidemiology covers time, place, and person.
• Person
– Age – Sex
Descriptive epidemiology
– Sex
– Marital status
– Race and etnicity
• Place
– International comparison of disease frequency – Regional variation within country
– Urba-rural differences
– Localized place comparisons
• Characterisctics of time
• Characterisctics of time
– Cyclic fluctuations – Point epidemic
– Secular time trends
Analytic epidemiology
• Analytic epidemiology is concerned with the search for causes and effects, or the why
and the how. Epidemiologists use analytic epidemiology to quantify the association between exposures and outcomes and to between exposures and outcomes and to test hypotheses about causal relationships.
– Experimental studies – Observational studies
Self-reported measuring Example1: ESPAD
(European School Survey Project on Alcohol and Other Drugs)
(Hibell et al 2009) www.espad.org
A main purpose of the ESPAD project is to collect comparable data on substance use among students in as many European
countries as possible.
• Target population:
• Target population:
– students who will be 16 years old in the data collection year, i.e. they should all be born in a specific calendar year
• Data collection instrument:
– The first ESPAD questionnaire was developed from the battery of questions tested by the Pompidou School
Survey Subgroup.
– A very large part of the first questionnaire was retained in later data collections
– The main part of the questionnaire constitutes of core – The main part of the questionnaire constitutes of core
questions to be used in all countries. In addition a number of module and optional questions were
included to be used at the choice of each country. In addition to this each country was free to add questions of special interest, provided those questions were not of
• Sampling
– The sample consists of randomly selected classes.
– It is recommended that, with some minor exceptions, each country, regardless of size, should draw a sample of about 2,800 students as a minimum
as a minimum
– Whenever possible it is recommended to include all grades with students born in the given year
• Field procedure
– The data collection in a country was planned to take place during a certain week, which should not be proceeded by any holiday, ensuring that the students referred to a “normal” week when answering the questions, i.e. no extraordinary alcohol or drug consumption due to any
alcohol or drug consumption due to any
celebration should be reflected in the answers – Data are collected by group administered
questionnaires, under the supervision of a teacher or a research assistant.
Methodological consideration
• Reliability
– Reliability, which is a necessary condition for validity, is the extent to which repeated measurements made under the same conditions produce the same result.
– ESPAD measured the reliablity by two measures:
• One is the inconsistency between two sets of questions measuring lifetime prevalence for different drugs.
measuring lifetime prevalence for different drugs.
• The other is the quotient between the proportion of students who replied to the “honesty question” that they had “already said” that they had used cannabis and the proportion who actually gave this answer.
• Validity
– The validity of answers is a major concern in survey research, particularly in surveys of
sensitive behaviours such as substance use. In ESPAD terms, validity could be said to be the degree to which the ESPAD survey (including methods of data collection) measures those methods of data collection) measures those aspects of students’ consumption of different substances that we intend to measure
• Student cooperation
• Student comprehension
• Rates of missing data
• Logical cinsistency
• Faking good
• Faking bad
• Construct validity
• Validity of the questionnaire
• Cultural context
• Cultural context
The analysis of available information strongly
suggests that the validity of the ESPAD
Self-reportes measuring Example 2: Alcohol
(Bloomfield, Hope, Kraus 2010
http://www.alcsmart.ipin.edu.pl/survey_methodo logy_-_projects_background_papers.html)
When measuring alcohol use as a risky
behaviour we can select from three main types of indicators.
• one describes the general drinking habit of a population or age group,
• other measures risk drinking
• other measures risk drinking
• the third describes alcohol related troubles.
Alcohol related troubles (dependence, addiction, alcohol related accidents)
Measuring general drinking habit
• Quantity-frequency (QF)
– It may be asked of varying periods: from a week to a year, depending upon the nature of the research
question and the main drinking pattern of the population under study
• Graduated frequency (GF),
– Numbers of drinks consumed on an occasion are grouped into graduated categories.
– The GF appears to work better with lighter drinkers and among those with more cognitive skills
• Short-term recall measures, such as the weekly recall (WR).
– respondents are basically asked to recall all alcohol they have consumed in a recent short period, such as the previous week.
– Due o the short term period respondents will be able to correctly recall all their consumption
able to correctly recall all their consumption – But, it is disadvantageous in capturing the full
patterns of infrequent drinkers
Measuring risky drinking habits
• Risky drinking
– heavy episodic drinking – binge drinking
– risky single occasion drinking – extreme drinking
These terms include more intensive, concentrated alcohol consumption, taking place within a short period.
– It is measured by 5/6 drinks in a row or in one occasion, a quantity
• Drunkenness
– a frequently used indicator of risk drinking.
– The main problem is its subjectivity.
Drunkenness might mean completely different state for child living in different drinking
cultures.
– Frequently used: combination of the indicator of frequency of drunkenness with the number of drinks to get drunk
Measures of alcohol related troubles
• Alcohol dependence and abuse
– Composite International Diagnostic Interview Substance Abuse Module (CIDI-SAM
– Alcohol Use Disorder and Associated Disabilities Interview Schedule (AUDADIS)
– Alcohol Use Disorders Identification Test (AUDIT) – CAGE
– CAGE
– Rapid Alcohol Problem Screen (RAPS4)
In the case of screening, the AUDIT or the RAPS4 appear more appropriate. But if one desires to approximate a diagnostic category, then CIDI, AUDADIS or an operationalisation of
Possible modes of survey adninistration in case of alcohol researches:
• face-to-face interview,
• telephone interview
• self-administered questionnaire (usually delivered
• self-administered questionnaire (usually delivered via post)
• web internet approaches
Mode of collection can affect
• non-response rates
– lowest in face-to-face surveys, higher in telephone surveys and the highest with mail surveys
• response bias
– face-to-face interview has traditionally been seen as the optimal mode, but there could be problems with
interview confidentiality and perceived social distance interview confidentiality and perceived social distance between interviewer and respondent
When telephone and face to face modes are well conducted, these two modes can lead to similar
Thank you for attention!
June 2011
