a4. Epk.causation

8/22/2019 a4. Epk.causation

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EPIDEMIOLOGI KLINIK

Introduction & Causation I

Bambang Udji Djoko Rianto, Sp.THT, M.Kes.


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Objective:

describe the concepts of cause

identify single & multiple causes

identify the proximity of cause to effect interactions among multiple causes

the establishing cause in individual studies

concepts of cause & effect as an association

hierarchy of research design: cause-effects

relationship


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evidence cause -effect cause in studies of population

type of evidence, relative strength

describe the concepts of risk identify the situations insufficient personalexperience

the purpose of the risk factors study

several scientific strategies for determining risks measures of effect for comparing risks


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The concepts of cause

something that brings about an effect or a result

cq. etiology, pathogenesis, or mechanisms

guiding for: prevention, diagnosis, & treatment


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Single and multiple causesKochs postulate: infectious agent is the cause

the organism:

must be present in every disease

must be isolated & grown in pure culture

when inoculated into susceptible animal, cause

specific disease

must be recovered from the animal & identified


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many diseases: Kochs postulate -

basic approach: particular cause result in disease

smoking cigarettes causes:

lung cancer, chronic obstructive pulmonary disease,

peptic ulcer

bladder cancer

coronary artery disease


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coronary artery disease caused by: cigarette smoking

hypertension

hypercholesterolemia

many factors act together to cause disease

web of causation


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Proximity of cause to effectThe occurrence of disease is determined by:

genetic

environmental

behavior factors

earlier in the chain

of diseases events

referred as origins of disease more likely to be investigated

by epidemiologists


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The knowledge of risk factors lead to:

effective treatments & prevention

can be applied without knowing the pathogenetic

mechanism of disease


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Interaction of multiple causesMultiple cause act together:

the resulting effect > effect of separate causes

elucidation of cause > difficult when play a part,

single one predominant interact, substantial impact, by changing 1/ small

number of causes


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the strength of cause-effect relationship between2 variables is different, according to the level of

some third variable: effect modifier

Effect modification:


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Association and cause

2 factors: the suspected cause & effect obviouslymust appear to be associated if they are to be

considered cause & effect

not all association are as causal


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Hierarchy of research designs

Randomized controlled trial:

to provide evidence cause & effect relationship for

treatments and prevention

to show a particular agent causes a disease sometime not possible to use this design

most potentially harmful agents or risk factors can

not be assigned at random

sometime would be unethical, and removal of

potential risk factors is rarely possible


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Randomized controlled trial (RCT):

there are problems of long latent periods & large

numbers of subjects needed in clinical medicine so, RCT rarely feasible when studying causes

of disease, and observational studies must be

used instead


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Cohort studies

the next best design to experiments to minimize the effects of selection & measurement

bias

Cross-sectional studies

are vulnerable

provide no direct evidence of the sequence of events

guard against selection bias, but subject to

measurement, and confounding bias


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Evidence that an association is cause & effect:

1. Temporality : cause precedes effect

2. Strength : large relative risk/ Odd ratio

3. Dose-response : larger exposure to cause associated

with higher rates of disease4. Reversibility : reduction in exposure associated

with lower rates of disease

5. Consistency : repeatedly observed by different

persons, places, circumstances &times


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6. Biologic plausibility : makes sense, according to

biologic knowledge of the

time

7. Specificity : one cause leads to one effect8.Analogy : cause-effect relationship

already established for a similar

exposure/ disease


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Establishing cause: studies of populations

characterized by average exposure of group

individuals: aggregate risk studies

people are classified by the general level of exposurein their environment

the main problem: potential bias (ecological fallacy)

people in a generally exposed group may not them-

selves be exposed to the risk there may be confounding factors


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In aggregate risk studies:

cause-effect relationship can be strengthened

if observation: made at > 2 points in time (before &

after)

In a time series study:

the effect is measured at various points in time

before and after the purposed cause has been

introduced

the effect varies in a similar fashion

if changes in purported cause are followed by

changes in purported effect, the association: less

spurious


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In multiple time series study:

suspected cause: introduced into several different

groups at various times measurements of effect and cause: same sequential

manner

effect regularly follows suspected cause at various

times & places: stronger evidence of relationship


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Weighing the evidence

If there is conflicting of cause-effect evidence: decide the weight of the evidence lies


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Types of evidence for cause-effect relationship:

Strength Design Finding

Strong Clinical trial Temporality

Cohort study StrengthCase control study Reversibility

Cross-sectional Dose-response

Aggregate risk Consistency

Case series Biologic plausibilityWeak Case report Specificity

Analogy


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Concept of risk

refers to the probability of some untoward event

used in a more restricted sense to describe the

likelihood that people who are without a disease,

but are exposed to certain factors (risk factors),

will acquire the disease


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Risk factors:

factors that are associated with an increased risk

of becoming diseases

Exposure to risk factor:

a person before becoming ill, come in contact

with or has manifested the factor in question

exposure: at single point in time, or over a period

of time characterizing of chronic exposure: ever exposed,

current dose, largest dose, total cumulative dose,

years of exposure, years since first exposure, etc.


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Various measure of dose tend to be related

each other:

some show an exposure-disease relationship

others do not

Appropriate measure:

based on all about biologic effects of exposure

pathophysiology of disease


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Situation in which personal experience is insufficient

to establish a relationship between exposure and

disease

Large & dramatic risks: easy to recognize the

exposure- disease relationship: follow rapid, certain,

and obvious way

- chickenpox, sunburn, aspirin overdose

In chronic disease: the relationship: far less obvious


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Situation in which personal experience is insufficient

to establish a relationship between exposure anddisease include:

long latency period between exposure-disease

frequent exposure to risk factor

low incidence of disease

small risk from exposure

common disease multiple cause of disease


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The purpose of the risk factors study

1. To predict the occurrence of disease

2. Assumed incidence of disease in exposed & non

exposed person to risk factor

- sometime risk factor as mark of disease indirectly by associate with other determinant(s)

- risk factor is not caused of disease: marker

3. In diagnostic process

4. To prevent disease


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Several scientific strategies for determining risk

1. Observational studies:- gathers data, simply observing events

- without playing in active part

- only feasible studying most question of risk

a. Cohort

- a group of people who have something in

common when they are first assembled, andwho are then observed for a period of time

to see what happen to them


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The basic design:

At risk exposure to risk factor disease

people at

risk

exposed

not exposed

time

yes

no

yes

no


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The likelihood of exposed persons to get the disease

relative to non-exposed persons is relative risk

: the ratio incidence in exposed persons to incidence in non

exposed persons


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b. Case control studies:

- compare the frequency of a purported risk

factor in a group of cases & a group of control

The basic design:

exposure to disease

risk factor

yes: cases

yes

no

no: controlyes

no

time

data collection present


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The measures effects for comparing risk

Several measures of association exposure-disease:

measures of effect:

1. Attributable risk (risk difference):

- what is the additional incidence (risk) of disease

following exposure, that experienced by peoplewho are not exposed ?

- the incidence of disease in exposed persons

minus the incidence in no exposed persons

- the additional incidence of disease related to

exposure, taking into account the background

incidence of disease, presumably from other

cause


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2. Relative risk:

- how many times more likely are exposed

persons to get the disease relative to non

exposed persons ?- the ratio of incidence in expected persons to

incidence in non exposed persons

- the strength association exposure-disease

- useful measure of effect for studies diseaseetiology


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3. Population risk (PR):

- how much does a risk factor contribute to

the overall rates of disease in groups of people

rather than individual ?

- for deciding which risk factors are particularlyimportant, & which are trivial to health of community

- in policy positions how to choose priorities for

deployment health care resources

- to estimate PR, take into account the frequencywith which members of a community are exposed

to a risk factor


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4. Population attributable risk:

- is a measure of the excess incidence of disease

in a community that associated with the occurrence

of a risk factor

- is the product of the attributable risk & prevalence

of the risk factor in a population


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5. Population attributable fraction

- the fraction of disease occurrence in a population

that is association with a particular risk factor- obtained by dividing the population attributable risk

by the total incidence of disease in the population


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Thank you

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a4. Epk.causation