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8 Community MedicinePrinciple of Epidemiology 11

Methods of Epidemiology

Dr. Siham GritlyUniversity of Bahri

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Epidemiologic methods are used for the identification of risk factors for disease and determination of optimal treatment approaches used in clinical practice

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Methods of Epidemiology

• Epidemiologic methods are used for;

• -the identification of risk factors for

disease

• -and determination of optimal treatment

approaches used in clinical practice.

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• In the study of communicable and chronic

diseases, the work of epidemiologists involves;

• study design,

• data collection

• and statistical analysis

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Epidemiological studies classified in two categories

• 1-observational studies (non experimental studies)

• A) descriptive studies• B) Analytical studies

• 2-experimental studies (intervention studies)• A) Randomized Controlled trial or clinical trail• B) 2-non randomized or non-experimental trials

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1-observational studies

• researcher observes association between exposure and disease, estimates and tests it

• 1-observational studies Include;

• A) descriptive studies

• B) Analytical studies

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A) descriptive studies

• Descriptive studies are usually the first phase

of an epidemiological investigation

• Observing the distribution of disease or health

related characteristics in human population

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• In Descriptive studies questions should be asked such as;

• When is the disease occurring----time distribution

• Where it is occurring------place distribution

• Who is getting the disease----persons distribution

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Procedures in Descriptive studies

• 1-defining the population to be studied

• 2-defing disease under study

• 3-describing the disease by;

• -time

• Place

• Person

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• 4-measurement of disease

• 5-comparing with known indices

• 6-formulation of an aetiological hypothesis

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• 1-defining the population to be studied• Descriptive study are investigation of

population not individual; include total number

• Sex• Age• Occupation• cultural

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• 2-defing disease under study;

• Specified the disease to be investigated

• The main objective to obtain accurate

estimate of disease in a population

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• 3-describing the disease by;

• The main primary objective of descriptive epidemiology

is to describe the occurrence and distribution of disease

by

• Time--

• Place

• person

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• 4-measurement of disease• The information should be available in terms

of• Mortality• Morbidity (incidence and prevalence)• distribution

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• 5-comparing with known indices

• Making comparisons between different

population, this is to ; identify groups who are

at risk for certain diseases

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• 6-formulation of an aetiological hypothesis

• Hypothesis should formulated in a manner that

that it can be tested

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• Hypothesis should specify the following• -the population- the characteristics of the

persons to whom the hypothesis to be applied• -the specific cause being considered• -the expected outcome• -the dose-response relationship• -the time-response relationship (time between

exposure to the cause observed)

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B) Analytical studies

• Analytical studies are the second major type of epidemiological studies

• In contrast to descriptive studies which look for the whole population the analytical studies look for individual within the population

• Main types of observational studies are;• Case control study• Cohort study

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Cohort or follow up

cohort study (prospective) ;

-individual exposed to particular factorsPresence or absence of particular diseaseIndividual unexposed to particular

factors

Typical analytical study designs: Cohort or follow up with individual as a unit of study. An example ; investigation of a cohort of smokers and non-smokers over time to estimate the incidence of lung cancer (prospective) ;

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case-control or case-references

Cases (disease present)

Control (disease absent)

Suspected or risk factors

Individuals with particular disease

Individual without particular disease

case-control or case-references with individual as a unit of study select subjects based on their disease status. It is a retrospective study.-factors present or absent---Observational

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• Cross-sectional or prevalence with individual

as a unit of study

• Ecological or correlation with population as

unit of study

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2-experimental studies or Interventional:

• Experimental studies are of two types• A-Randomized Controlled trial or clinical trail

• B-non randomized or non-experimental trials • -field trials or community intervention studies• -Community trial

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A)-Randomized Controlled trial or clinical trail

• A study design that randomly assigns participants into an experimental group or a control group.

• As the study is conducted, the only expected difference between the control and experimental groups in a randomized controlled trial (RCT) is the outcome variable being studied.

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• Design of randomized control trial;• The protocol; • Selecting reference and experimental population

(make necessary exclusions)• Randomize of two• 1-experimental group• 2-control group• Follow up • assessment

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• Advantages• No population bias

• Results can be analyzed with well known statistical tools

• Populations of participating individuals are clearly identified

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• Disadvantages• Expensive in terms of time and money

• biases: the population that participates may not be representative of the whole

• Does not reveal causation

• Loss to follow-up

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B-Non-randomized controlled trial

• An experimental study in which people are

allocated to different interventions using

methods that are not random.

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Study Designs: Types

• Qualitative

• Quantitative

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Qualitative QuantitativeDefinition a systematic

subjective approach used to describe life experiences and give them meaning

a formal, objective, systematic process for obtaining information about the world. A method used to describe, test relationships, and examine cause and effect relationships.

Goals To gain insight; explore the depth, richness, and complexity inherent in the phenomenon.

To test relationships, describe, examine cause and effect relations

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Qualitative QuantitativeCharacteristic •Soft science

•Focus: complex & broad•Subjective•Basis of knowing: meaning & discovery•Develops theory•Shared interpretation•Communication & observation•Basic element of analysis: words•Individual interpretation•Uniqueness

Hard scienceFocus: concise & narrow

ObjectiveBasis of knowing: cause & effect, relationshipsTests theoryControlInstruments

Basic element of analysis: numbersStatistical analysisGeneralization

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Objective vs Subjective

• Objective is a statement that is completely unbiased.

• It is confirmable by looking up facts or performing mathematical calculations.

• scientific facts are objective as are mathematical proofs; essentially anything that can be backed up with solid data.

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• Subjective is a statement that has been colored by the character of the speaker or writer.

• It often has a basis in reality,

• It cannot be verified using concrete facts and figures

• Subjective : opinions, interpretations, and any type of marketing presentation are all subjective.

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references

• Park's Textbook of Preventive and Social Medicine 21 Edition, by K. PARK