Lecture of epidemiology

Amany R.Abo-El-SeoudProf. of Community MedicineZagazig University, EGYPT

RESEARCH METHODOLOGY(Epidemiological methods)

Define: epidemiology, its uses. Recognize the different types of

epidemiological research methods. Explain how to design scientific researches

by the different methods Compare the different research methods

(advantages and disadvantages)

The intended learning objectives are:

Why do we do medical research?

1. Describe the health status of the population in certain community and subsequently diagnose its health problems.

2. Discover the causes of diseases and determinants of ill or good health.

3. Discover the risk factors that predispose to diseases of unknown etiology.

4. Complete the clinical picture of diseases from beginning of pathological changes till cure or occurrence of complications.

5. Evaluate the effectiveness of health services or test the validity of diagnostic tests or evaluate the prognosis

Objectives of medical research:

◦ Disease does not occur randomly ◦ Disease has identifiable causes which can be

altered and therefore can be prevented from developing

Health is a state of equilibrium between:

Agent Host

Environment

Important Assumptions:

Define: epidemiology, what are its uses

1st objective

Study of epidemics & epidemic disease (Stedman’s medical dictionary)• The science making the obvious obscure (epidemiologist)• The worst taught in medical school (medical student)

EPIDEMIOLOGY

The word epidemiology comes from the Greek words epi, meaning “on or upon,” demos, meaning “people,” and logos, meaning “the study of.” “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 control of health problems.

EPIDEMIOLOGY

describe the natural history of diseases explore disease causality

- direct: biological mechanisms of disease- indirect: social and environmental causes of disease

provide disease surveillance - essential for evaluating community health problems

and setting disease control priorities evaluate diagnostic testing

- evaluate validity, sensitivity, specificity- to set cutoff points for abnormalities

evaluate prognosis

- by identifying prognostic factors

Uses of Epidemiology in Clinical

Medicine

Recognize the different types of epidemiological

research methods.

2nd Objective

Types of epidemiological studies

Quantitative studies

Qualitative studies

- Observational -Experimental

- Phenomenology (phenomena)– Ethnography (cultures, people)

Development of concepts which help us to understand social phenomena in natural settings, giving due emphasis to the meanings, experiences, and views of all the participants

Explaining complex phenomena not amenable to quantitative research

Method : Focus group, observation, interviewApplication (examples) Doctor-patient relationship, treatment

compliance, clinical decision making process, issues on health service organization

and policy issues

Qualitative study

Two main categories:

1. Observational studies (researcher not intervene) : cross-

sectional(descriptive)– retrospective (case control) – prospective (cohort)

2. Experimental studies (researcher intervene) exposure status is assigned

(intervention)

Types of quantitative Studies

OBSERVATIONAL STUDIES According to time of research

Cross-sectiona

lCase -series

RetrospectiveCase control

Prospective

CohortFollow up

history Time now Future

Descriptive

Cross-sectional

Case series/study

Analytical

Case-control

Cohort

OBSERVATIONAL STUDIESin relation to research question

Descriptive Epidemiology deals with the questions: Who, What, When, and Where?

Analytic Epidemiology deals with the remaining questions: Why and How?

Descriptive vs. Analytic Epidemiology

Study the prevalence of diabetes in Zagazig Study the relation between smoking and

lung cancer Study women satisfaction for antenatal care Study the effect of obesity on fetal outcome Study the risk of iodine deficiency on

mental retardation Study suggestions for improvement of in zagazig hospital

Quiz: choose type of ES

Explain how to design scientific researches

by the different methods

3rd Objective

Specified population

Health relatedproblem

Distribution

Risk factors

Frequency Pattern

Health events in population

Numbers & ratesPrevalenceIncidence

Time, person, placeWhen , who, where

RISK FACTORS

Social

Cultural

Behavioral Biological

Physical

Descriptive epidemiological study of any disease can provide these knowledge: e.g.Food borne epidemic, TB, parasitic infestation

Pattern =Time , person , place Frequency = prevalence & incidence rates

May be : Determinants = risk factors

Descriptive epidemiology

whatwhatwhenwhen

whowhowhere

where

Descriptive

Cross-sectional

Case series/study

Analytical

Case-control

Cohort


1- Prevalence/Cross-sectional/ Surveys measures prevalence of disease or

incidence of an event Investigation of epidemic

2- Case report / case series

TYPES OF DESCRIPTIVE STUDIES

Useful for assessing the burden of disease within a population

Valuable for planning & follow up

Prevalence rate= number of cases (old & new)

Number examined in the same time & place

Study Prevalence rate

no. of new cases of disease over a specific period of time

Incidence = ----------------------------- no. of persons at risk of

disease over that specific period of time

Study Incidence rate

Prevalence and Incidence

= prevalent cases = incident cases = deaths or recoveries

Prevalence is a function of the incidence of disease and the duration of disease

Prevalence and Incidence

Prevalence & incidence calculation.

QUIZ

Descriptive

Cross-sectional

Case series/study

Analytical

Case-control

Cohort


Case reportunit of study: single person with a

diseaselimitation: based on experience of a

single personprovides first clues in the identification

of a disease or adverse effects of exposure

(halothane induced hepatitis)

Types of Descriptive Studies (cont.)

Case series unit of study: group of persons with

a similar disease Uses:

o formulation of criteria for diagnosiso formulation of indications for

treatmento identification of prognostic factorso determination of survival rates

TYPES OF DESCRIPTIVE STUDIES

a-Cheap, rapid, easy b-Can use large sample of the population. c-Assess health status, and health problems

and indicate priorities for health care planning. Assess customer’s satisfaction for health care.

d-Provides the base-line data for further studies if the problem is not studied before.

e- Cross sectional study is the most convenient first step in the investigation of the cause of the outbreak or epidemic.

Advantages of cross-sectional studies

Sequence of events cannot be ascertained

Not useful for diseases of short period of time

Not practical in studying rare diseases

Case reports are susceptible to biasCase reports can not be used to make treatment decisions.

Disadvantages of cross-sectional/ surveys/ Case Series studies

Descriptive

Cross-sectional

Case series/study

Analytical

Case-control

Cohort


Epidemiology and laboratory science converge to provide the evidence needed to establish causation. A team of epidemiologists were able to identify a variety of risk factors during an outbreak of a pneumonia or cholera epidemic etc..

Analytical studies search for causes

Epidemiology Laboratory

Evidence of causation

Two groups: one is the case group “diseased’ and the other is the control group ‘healthy".

- Both diseased group and the control group must be matched in everything except the disease i.e matched in age, sex, socioeconomic class, occupation, residence etc.

-The collection of data is retrospectively i.e we ask both cases and controls about their past exposure of the risk factor under study.

-The proportion of those exposed to a certain factor in each group is compared.

ANALYTIC STUDIESHow to design Case-control Study?

Requirements for valid resultsCases must be representative of all those with disease and clearly defined.

Controls must be representative of all those without the disease and come from same community or source as the cases.

There must be a control ( 1 or more) for each case

CASE-CONTROL STUDIES

Case-Control Studies

Had Exposure No Exposure

StudyPopulation

Cases Controls

No ExposureHad Exposure

Analysis of case control studies

Used to find a relation between disease and exposure

Outcome (disease)

Exposure(risk)

diseased healthy Total

Yes a b a + b

No c d c + d

Total a + c b + d a + b + c + d

Odd’s Ratio (OR)proportion of those with history of

exposure to the factor among the cases (a/a+c) is compared to those with history of exposure (b/b+d) to the factor among the controls

OR = ad/bc

Analysis of case-control studies

Odds Ratio Example

Autism

MMR Vaccine? Yes No

Total

Yes 130 115 245

No 120 135 255

Total 250 250 500

a x d 130 x 135OR = = = 1.27

b x c 115 x 120

How to interpret “OR”?

Disease Risk Odds Ratio 95% CI p-value

Cancer lung Smoking 2.4 1.3 – 4.4 0.004

Cancer breast Trauma 1.9 1.3 – 2.8 0.001

Infarction Obesity 1.3 1.0 – 1.7 0.04

Duodenal ulcer HP 3.7 1.0 – 5.7 0.04

Diabetes m. Viral infection 0.9 0.5 – 1.8 0.80

Cancer cervix Genital warts 0.4 0.2 – 1.0 0.05

advantages Good for unusual or

rare diseases Quick, easy, cost-

effective Can use secondary data

on disease More easily replicated Suitable for more than

one risk at a time Can test hypotheses

disadvantages Uncertainty is exposure-

disease time relationship Representativeness of

cases or controls Memory problems Rare exposure Survivor problem Bias potential (selection)

Case control studies

QUIZWhich of these research questions can be answered by case-control study? how?1- Evaluation of performance in a health unit2-Relation between vitamin B deficiency &nerve conduction3- Relation between X (rare disease) and Y risk factor4- Relation between cancer skin and Y rare exposure risk

Design case-control study to find the relation between contraceptive pills and deep venous thrombosis.

Calculate odds ratio for this relationship:

QUIZ

Liver cirrhosis No cirrhosis

Bilharziasis 40 20

No bilharziasis 10 80

Descriptive

Cross-sectional

Case series/study

Analytical

Case-control

Cohort


groups of subjects are chosen on the basis of having been exposed to a factor or not

groups are followed up to identify those who develop the disease or outcome

TYPES OF ANALYTIC STUDIES(2) Cohort Studies = follow up study

Usesto test prognostic factorsto directly measure risk of development of disease or outcome

provide more definitive information about disease etiology

preferred for study of rare exposures

COHORT STUDIESfollow up / prospective

Cohort Studies

Disease No Disease

HealthyPopulation

Exposed Non-exposed

No DiseaseDisease

Exposure isself selected

Follow throughtime

Analysis: Assess the strength of an association between an exposure and the outcome of interestRelative Risk or Risk Ratio(RR)

proportion of subjects with the disease or outcome among the exposed (a/a+b) is compared to proportion of subjects with the disease or outcome among the unexposed (c/c+d)

RR = a/a+b ÷ c/c+d

COHORT STUDIES

Attributable Risk (AR)estimate of the amount of risk that is attributable to the risk factor

AR = a/(a+b) - c/(c+d)

Relative Risk Example

Escherichia coli

hamburgerYes No

Total

Yes 23 10 33

No 7 60 67

Total 30 70 100

a / (a + b) 23 / 33RR = = = 6.67

c / (c + d) 7 / 67

Advantagesprovides direct estimate of riskTime sequence can be ascertained less biases of recall and observation

controls easier to assemblevariations in exposure can be followed-up

unsuspected effects of the exposure may be observed

COHORT STUDIES

Disadvantagesmore expensivefollow-up period may be longhigh drop out ratelarge sample size requiredchange in exposure rates over long

periods of time

COHORT STUDIES

Types of epidemiological studies

Quantitative studies

Qualitative studies

- Observational-Experimental

- Phenomenology (phenomena)– Ethnography (cultures, people)

Two main categories:

1. Observational studies (researcher not intervene) : cross-sectional(descriptive)– retrospective (case control) – prospective (cohort)

2. Experimental studies (researcher intervene) exposure status is assigned

(intervention)

Types of quantitative Studies

Three different ways of classifying intervention studies

I. Based on population studies◦ Clinical trial: on patients in clinical settings ◦ Field trial: on healthy people in the field ◦ Community trial: on the community as a whole

II. Based on design ◦ Uncontrolled trial: no control (self-control/cross-

over)◦ Non-randomized controlled: allocation not

random◦ Randomized control: Allocation random

Experimentalintervention studies

Randomization: random allocation of study subjects

into treatment & control groups Outcome/endpoint

Improvement ( desired effect) and side effectsMust be exactly defined Measured comparably in all study groups

Blinding: Denying information on treatment/control status. Single – subjects (placebo effect) Double - subjects & investigatorsTriple blind - subjects & investigators & statisticians

Experimental studies

New treatment Current treatment/no treatment

Improved Not improved

Improved Not improved

Intervention

Outcome

Selection of subjects -similar features -inclusion/exclusion criteria

Allocation of subjects

Data collectionMasking (blinding)

Randomized controlled trial

Define population

Evaluate new forms of therapy and prevention

Treatment or drugs

Health care technology - device

Methods of primary prevention - screening

Organizing and delivering health services

(community trial)

Impact of new policies in health care and health care

financing (community trial)


Advantages:

Strongest design - randomization, minimal

selection bias

Must be ethical - no harmful intervention,

no poor clinical outcome


Disadvantages:

Difficult for intervention in rare disease / rare

outcome

Participation of subjects is crucial Non-compliance (people who complaint are very

different from those who are not)* Drop-out: not adherence to experimental regimen,

loss to follow-up* Drop-in: not adherence to control regimen Compliance -Need monitoring Most costly


Types of randomized clinical trials

Surgical Medical

randomized

randomized

Refuse surgery Require surgery

No surgerySurgery

Most common Parallel A B

Cross-over

• Planned – wash out

• Unplanned

Classification of Study Designs

Source: Grimes DA, Schulz KF. Lancet 2002; 359: 58

1. Research questions

2. Occurrence of disease / exposure -rare/ common

3. Ethical issue

4. Resources- money, manpower, machine

Several designs may well be suitable for aparticular study. Choice must then be guided

byconsiderations of strength of design, cost

and ethics.

Which study design?

Study design Treatment Diagnosis Prognosis Agreement Classification

RCT ## - - - -COHORT # - ## - ##CASE-CONTROL - - - - -CROSS SECTIONAL - ## - ## ##CASE SERIES # # # - #

SummaryDesign of research depends on research QTreatment efficacy/safety = RCTDiagnostic methods, prevalence = cross- sectionPrognosis- outcome = cohortsatisfaction measurement = cross- sectionalrelation between risk and disease = case-control, cohort

1. Randomized controlled trial

2. Cohort study

3. Case control study

4. Cross sectional study

5. Case report or case series

6. Experimental animals

7. Qualitative research

Types of study designs

Design a research to find out the relation between obesity and diabetes (use 2 different methods)

Design a research to find out which is better drug A or drug B for hypertension

QUIZ

Sampling techniquesAdvantages of sampling

Types of sampling

Advantages Disadvantages Requirements Validity

Screening test

Gold standard test

test diseased healthy Total

positive a b a + b

negative c d c + d

Total a + c b + d a + b + c + d

THANK YOU

Lecture of epidemiology

Health & Medicine

Transcript of Lecture of epidemiology