NAEM LECTURER EPIDEMIOLOGY A.pdf

2. Introduction
• Epidemiology is often described as the basic science and an integral
component of public health.
• It is a quantitative discipline that relies on a working knowledge of
probability, statistics, and sound research methods.
• It is also a method of causal reasoning based on developing and
testing hypotheses grounded in various scientific fields to explain
health-related behaviors, issues, and events.
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3. • Epidemiology comes from the Greek words: epi, meaning on or
upon, demos, meaning people, and logos, meaning the study of. In other
words, the word epidemiology has its roots in the study of what happens to
a population.
• Many definitions have been proposed for it, but the following is one of the
most comprehensive:
“Epidemiology is the study of the distribution and determinants of health-
related issues or events in specified populations, and the application of this
study to the control of health problems.”
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4. Epidemiology as a field of “study”
• Epidemiology is data-driven and relies on a systematic and unbiased
approach to the collection, analysis, and interpretation of data.
• Basic epidemiologic methods tend to rely on careful observation
and/or the use of valid comparison groups to assess whether what was
observed e.g., the number of cases of a disease in a particular area
during a particular period, differs from what might be expected.
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5. Epidemiology studies “distribution”
Epidemiology is concerned with the frequency and pattern of health
events in a population:
• Frequency refers not only to the number of health events such as the
number of cases of meningitis or diabetes in a population, but also to
the relationship of that number to the size of the entire population.
• Pattern refers to the occurrence of health-related events by time,
place, and person.
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6. Epidemiology tries to identify “determinants”
• A Determinant is any factor, whether event, characteristic, or other
definable entity, that brings about a change in health or health-related
conditions.
• Epidemiology is also used to search for determinants, which are
causes and other factors that influence the occurrence of disease and
other health-related events.
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7. Epidemiology encompasses all “health related
issues or events”
• Epidemiology was originally exclusively focused on epidemics of
communicable diseases but was expanded to address endemic
communicable and non-communicable diseases.
• By the middle of the 20th Century, additional epidemiologic methods had
been developed and applied to the study of chronic diseases, injuries, birth
defects, maternal-child health, occupational health, and environmental
health.
• Currently, with the recent explosion in molecular methods, epidemiologists
can make important strides in examining genetic and other molecular
markers of disease risk.
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8. Epidemiology studies “specified populations”
• Although epidemiologists and direct health-care providers (clinicians) are
both concerned with occurrence and control of disease, they differ greatly in
how they view “the patient.”
• The clinician is concerned about the health of an individual; the
epidemiologist is concerned about the collective health of the people in a
community or population.
• In other words, the clinician’s “patient” is an individual; the
epidemiologist’s “patient” is the community.
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9. Epidemiology is an “applied art/science”
• Epidemiology is not just “the study of” health in a population; it also
involves applying the knowledge gained from these studies to
community-based practice.
• Consequently, epidemiologists use scientific methods, epidemiologic
judgment, and their understanding of local conditions in “diagnosing”
the health of a community and proposing appropriate public health
interventions to control and prevent disease in the community.
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10. Uses of Epidemiology/Epidemiological data
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11. 1. Assessing community
health and/or utilization
of available health
services
• Public officials and other
stakeholders can use
epidemiological data to aid decision
making on issues relating to public
health.
• Epidemiological data may also be
collected and analyzed to
determine whether health services
are available, accessible, effective,
and efficient.
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12. 2. Making individual
decisions
• Many individuals may not realize
that they use epidemiologic
information to make daily
decisions affecting their health.
• For example, when individuals
decide to quit smoking or use a
condom, they are being
influenced, consciously or
unconsciously, by epidemiologists’
assessment of risk.
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13. 3. Completing a
clinical picture
• Epidemiologists also contribute to
physicians’ understanding of the
clinical picture and natural history
of diseases.
• For example, epidemiologists,
clinicians, and researchers around
the world collaborated to
characterize SARS and COVID-19
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14. 4. Searching for
causes
• A lot of epidemiologic research is
devoted to searching for causal
factors that influence one’s risk of
disease.
• Ideally, the goal is to identify a
cause so that appropriate public
health action might be taken..
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15. Types of Epidemiology
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16. 1. Descriptive epidemiology
• Descriptive epidemiology provides a way of organizing and analyzing
data on health and disease in order to understand variations based on
time, place, or person.
• In this type of epidemiology, data is collected usually from a single
group/population, collated by time, place, or person and graphically
represented using charts, maps and tables.
• This type of epidemiology can provide important clues to the causes
and factors increasing the risk of a disease/ health-related condition.
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17. Example of a descriptive epidemiology chart showing patients involved (by gender and
age) in a 2014 cholera outbreak in Kaduna state
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18. Example of a descriptive map showing security challenges in Nigeria by location
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19. Example of a descriptive epidemiology chart showing trends in age-adjusted death rates for
leading chronic diseases in the United States from 1960 - 2007
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20. 2. Analytic epidemiology
• Analytic epidemiology is concerned with the search for causes and/or
effects, which it does through comparison between 2 or more groups
• Epidemiologists use analytic epidemiology to quantify associations
between exposures and outcomes and to test hypotheses about causal
relationships.
• While it has been said that epidemiology by itself can never
completely prove that a particular exposure caused a particular
outcome, it often provides sufficient evidence to take appropriate
control and prevention measures.
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21. Overview of Epidemiological
Methods
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22. Class Quiz
• What Epidemiological methods and their examples do you know or
are familiar with?
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23. Observational
methods
Experimental
methods
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24. Observational methods
• Case reports/ series
• Ecological studies
• Cross-sectional studies
• Cohort studies
• Case-control studies
Experimental methods
• Clinical trials
• Community trials
• Field trials
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25. Methods used
to collect data
Type of
epidemiology
Topic Epidemiology
Analytical
Observational
methods
Cross-sectional studies
(rare)
Cohort studies
Case-control studies
Experimental/interve
ntional methods
Clinical trials
Community trials
Field trial
Descriptive
Observational
methods
Case reports/series
Ecological studies
Cross-sectional studies
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26. 1. Case Report
• A case report is a detailed
description of disease
occurrence in a single person.
• Unusual features of the case
may suggest a new hypothesis
about the causes or
mechanisms of disease.
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27. 2. Case Series
• A case series is a report on the
characteristics of a group of subjects
who all have a particular disease or
medical condition.
• The "series" may be small (less than 10
“cases”) or it may be large (hundreds or
thousands of "cases").
• While common features among the
cases may suggest hypotheses about
disease causation, the chief limitation of
these types of studies (i.e., case reports
and series) is that they have no
comparison group.
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28. 3. Ecological studies
• Ecologic studies assesses the overall
frequency of disease in a series of
populations.
• These studies are unique in that the
analysis is not based on data on
individuals. Instead, the data points are
the average levels of exposure and the
overall frequency of disease in a series
of populations.
• The major limitation of this type of
study is known as “the ecological
fallacy”
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29. 4. Cross-sectional studies
• The cross-sectional study tends to assess
the presence (prevalence) of the health
outcome at a single point of time.
• They may also be referred to as
prevalence studies.
• Cross-sectional studies are used
routinely to document the prevalence of
health behaviors (e.g., smoking), health
states (e.g., vaccination against
measles), and health outcomes,
particularly chronic conditions
(hypertension, diabetes etc.)
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30. 5. Cohort studies
• In a cohort study the epidemiologist
records whether each study
participant is exposed or not, and
then tracks the participants over
time to see if they develop the
disease of interest.
• These studies can be prospective or
retrospective
• Limitations of this type of study
include issues with bias and loss of
participants during follow-up
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31. Class Quiz
• What types of bias in epidemiological study are you familiar with
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32. Types of bias and their Definitions
• Observer bias: Observer bias is said to occur
in an epidemiological study when an
investigator’s or observer’s prior knowledge
or prejudices unduly influence what he
perceives or records in a study. This will
therefore affect the outcome of the study.
• Recall bias: This type of bias occurs in
controlled trials when there is a systematic
difference between participants in the study
groups (other than the intervention being
studied).
• Social desirability bias: Describes a scenario
in which some individuals within a target
population are more likely to be selected for
inclusion into a study than others. For
example, if participants are asked to
volunteer for a study, it is likely that those
who volunteer will not be representative of
the general population, threatening the
generalizability of the study results.
• Sampling bias:This type of bias occurs where
respondents to surveys tend to answer in a
manner they feel will be seen as favorable by
others, for example by over-reporting positive
behaviors or under-reporting undesirable
ones.
• Allocation bias:This type of bias is an issue
when study participants need to accurately
remember past events. It occurs when the
information provided about exposure differs
between the study groups.
• Attrition bias:This type of bias is as a
result of the investigator’s prior knowledge
of the hypothesis under investigation or
knowledge of a study participants’
exposure or disease status. Such
information influences the way the
investigator collects or measures
information or interprets it.
•
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33. 6. Case-control studies
• In a case-control study, investigators
enroll two groups of people [1 group
with a disease (cases), the other without
the disease (controls)].
• Investigators then compare previous
exposures between the two groups (i.e.,
case control studies are only
retrospective).
• The key in a case-control study is to
identify an appropriate control group
that is comparable to the case group
(i.e., proper matching of cases and
controls).
• Limitations include issues with bias and
confounding
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35. 7. Community
trials
• Community trials address the
efficacy of preventive
interventions applied at the
group level.
• These types of trials are
generally conducted when the
intervention inherently operates
at a group-level (e.g., changing a
law or policy) or because it
would be difficult to give the
intervention to some people in
the group while withholding it
from others.
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36. 8. Clinical trials
• Clinical trials assess preventive
interventions or evaluate new
treatments for existing diseases
in individuals.
• They could either be
randomized controlled trials or
non-randomized/quasi
experimental trials
• Clinical trials must enroll enough
participants and follow them for
an adequate period.
Consequently, they can take a
long time and are very
expensive to conduct.
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37. Hierarchy/levels of Evidence
• In recent years, a lot of emphasis has been placed on finding and
using scientific data/evidence to make healthcare/clinical decisions
i.e., Evidence-based medicine (EBM).
• As the name suggests, evidence-based medicine (EBM), is about
finding evidence and using that evidence to make clinical decisions.
To make this easier to do, scientific evidence was classified based on a
hierarchical system known as the levels of evidence.
• These levels are represented by a pyramid shape. The higher up the
source of evidence on this pyramid, the better its quality.
Consequently, all healthcare practitioners are encouraged to find the
highest level of evidence to answer their clinical questions.
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40. Pharmacoepidemiology
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41. Background
• Pharmacoepidemiology is a branch of epidemiology that deals with
the study of the use and effects of drugs in large numbers of people.
• Just as the name implies, it combines clinical pharmacology with
epidemiology, and applies epidemiological techniques to study drug
use in large populations.
• Pharmacoepidemiological studies may be used to describe and
quantify drug use patterns and adverse drug effects.
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42. Roles for pharmacists with respect to
pharmacoepidemiology
• A practicing pharmacist is in a prime position to help identify issues or
problems that a pharmacoepidemiologist may want to study further.
• Pharmacists can also provide guidance on the development of
reporting forms and databases, which provide data for
pharmacoepidemiology studies.
• Pharmacists should be users of pharmacoepidemiology research
principles and findings and help to disseminate their results
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43. References
• Barratt, H., Kirwan, M., & Shantikumar, S. (2018). Biases and confounding. Retrieved November 7, 2022,
from https://www.healthknowledge.org.uk/public-health-textbook/research-methods/1a-
epidemiology/biases#:~:text=More%20than%2050%20types%20of,information%20bias%20and%20selection
%20bias.
• CDC. (2012). Principles of Epidemiology in Public Health Practice: An Introduction to Applied Epidemiology
and Biostatistics (3rd ed.). Atlanta, Georgia: US Department for Health and Human Services.
• Gerstman, B. B. (2013). Epidemiology kept simple: An introduction to traditional and modern epidemiology
(3rd ed.). Chichester, UK: Wiley-Blackwell.
• LaMorte, W. (2020, September). PH 717 Module1B: Descriptive epidemiology and descriptive statistics.
Retrieved November 7, 2022, from https://sphweb.bumc.bu.edu/otlt/MPH-Modules/PH717-
QuantCore/PH717-Module1B-DescriptiveStudies_and_Statistics/index.html
• Mann, C. J. (2003). Observational research methods. research design II: Cohort, Cross Sectional, and case-
control studies. Emergency Medicine Journal, 20(1), 54-60. doi:10.1136/emj.20.1.54
• Song, J. W., & Chung, K. C. (2010). Observational studies: Cohort and case-control studies. Plastic and
Reconstructive Surgery, 126(6), 2234-2242. doi:10.1097/prs.0b013e3181f44abc
• West-Strum, D. (2011). Introduction to Pharmacoepidemiology. In Understanding pharmacoepidemiology
(pp. 1-12). New York, NY: McGraw-Hill Medical.
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