Epidemiological Studies: Analytical Studies II – Cohort Studies

Observational Analytical Studies

Why is an individual affected by a particular disease and another is not?

Observational analytic studies are needed to uncover associations between:

Risk Factors → Disease(s), injuries, impairment, disability

Beneficial interventions → Improvement in health status (mortality,

morbidity, quality of life, etc.)

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descriptive observational →

case report

Case series

Correlational studies

Cross-sectional studies

observational analytical

case control

cohort study

Types of observational analytical studies are:

1. case-control studies

2. Cohort studies

I’m only observing not intervening and there’s no experiment

Types of interventional/ experimental analytical studies are: 1.Randomized controlled trials 2.Non-randomized controlled trials

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Types of interventional/ experimental analytical studies are:

Types of interventional/ experimental analytical studies are: 1.Randomized controlled trials 2.Non-randomized controlled trials

Interventional studies asses

s benefits and harms of interventions

COHORT means:
- Group of people in forward motion

over time (from exposure to outcome)

→ outcome : Most commonly a disease

→ Exposure → Potential risk factor or

potential determinant or

potential etiological factor

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COHORT means:

COHORT means:
- Group of people in forward motion

over time (from exposure to outcome)

→ outcome : Most commonly a disease

→ Exposure → Potential risk factor or

potential determinant or

potential etiological factor

E → P

COHORT
you follow a rsik factor exposure to see disease

synonyms of cohort studies?

Follow-up study

· Longitudinal study

. Prospective study

Follow-up study

· Longitudinal study

. Prospective study

synonyms of cohort studies

Cohort Study Design

• A study in which an exposed group and a non-exposed group are followed over time to determine who develops the disease of interest.

• A cohort is a group of people sharing a common characteristic

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Cohort Study Design

defintion?

Cohort Study Design

• A study in which an exposed group and a non-exposed group are followed over time to determine who develops the disease of interest.

• A cohort is a group of people sharing a common characteristic

cohort always start with exposure

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cohort always start ???

cohort always start with exposure

casue → effect

cohort

in cohort we eed what people?

exposed
non-exposed

In cohort study always start with a disease-free population then divide them to exposed and non exposed

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what can be calculate in cohort study?

RR
AR
Population totAL

smokers
non-smokers
folloow them 2 years to see result
type of what study?

cohort study

in cohort we can start by
1- start two groups
exposed
on-exposed

2- او نبدا ببوبيوليشن طبعا مافيها المرض

واقسمها كل مره على حسب دراستي مثلا مره ابغا اقارن بالعمر ف اقسمهم على اعمارهم ومره ابغا اقارن

حسب التدخين ف اقسم مدخنين وغير مدخنين (بس هم بالاساس مجموعه وحده كل مره اقسمهم بطريقه ثانيه)

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Outcome Assessment After the follow up period, the endpoints (outcomes) of interest could be:

1. Development of disease

2. Freedom of disease

3. Death

4. Lost to follow-up

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outcome of cohort study are?

Outcome Assessment After the follow up period, the endpoints (outcomes) of interest could be:

1. Development of disease

2. Freedom of disease

3. Death

4. Lost to follow-up

Whatwasarequirement to be included in the cohort? bermingham

free of CVD

Discoveries All associated with CVD • High blood pressure • High cholesterol • Smoking F • Obesity, diabetes, physical inactivity • Concept of risk factories and risk prediction models • Benefits of lifestyle modification

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Types of Cohort Studies:

• .Prospective cohort study E → P

• Non- concurrent (retrospective or historical) cohort Study → In this type, the follow-up period between exposure to the risk factor and the development of disease has already occurred (or is still under way). In this method we use records → TO DETECT PRESENCE OF A DISEASE

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• Non- concurrent cohort study another names

• (retrospective or historical) cohort Study

• Non- concurrent (retrospective or historical) cohort Study → what do we mean by that?

• Non- concurrent (retrospective or historical) cohort Study → In this type, the follow-up period between exposure to the risk factor and the development of disease has already occurred (or is still under way). In this method we use records

what we use in the Non- concurrent (retrospective or historical) cohort Study ???

• Non- concurrent (retrospective or historical) cohort Study → In this type, the follow-up period between exposure to the risk factor and the development of disease has already occurred (or is still under way). In this method we use records

An example is the cohort of persons in Hiroshima, Japan. It is taken from records. Follow up period occurred in past
wht type of study?

• Non- concurrent (retrospective or historical) cohort Study → In this type, the follow-up period between exposure to the risk factor and the development of disease has already occurred (or is still under way). In this method we use records

Two main types of follow up in cohirt study:

1.Active : in which we examine the cohort members periodically after they have entered the study cohort.

2.Passive: records of the hospitals at which cohort members who seek care can be monitored.

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Two main types of follow up in cohirt study:

1.Active :

2.Passive: .

Two main types of follow up in cohirt study:

1.Active : in which we examine the cohort members periodically after they have entered the study cohort.

2.Passive: records of the hospitals at which cohort members who seek care can be monitored.

Passive:

Passive: records of the hospitals at which cohort members who seek care can be monitored.

Active :

Active : in which we examine the cohort members periodically after they have entered the study cohort.

prospective
2012 → 2024 → 2036

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retrospective cohort study
→ we are in 2012
go back to 1992 for info

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What can we calculate from a cohort study?

RR

AR

incidence rate exposed or non exposed

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incidence rate of exposed

a / a+b

incidence rate of NON- exposed

C / C+D

Incidence (total population) :

a + c / a+b+c+d

Relative risk →

exposed / non-exposed
( a / a+b ) / ( c/ c+d)

Atrributed risk ?

exposed - non-exposed
( a / a+b ) - ( c/ c+d)

Atrributed risk among expposed?

exposed - non-exposed
( a / a+b ) - ( c/ c+d)

______________________

( a / a+b )

Atrributed risk among population?

IP - INON
——————

IP

Incidence of IHD among smokers

a / a+b

Incidence of IHD among non-smokers (non-exposed)

c / c+d

Incidence of IHD among the study population (total population

a + c / a + b + c +d

Relative risk

exposed / non-e

AR

EXPOSED - nonexposed

Attributable risk among exposed (etiologic fraction)

exposed - non-exposed / exposed

AR

RR

incidence of exposed or nonexposed in what?

in cohort study

odd ratio = a + d / a + b+ c+d

in case-control

Follow up period (e.g. 2000 till 2010

in cohort

Start by exposure (e.g. smoking and IHD: start in 2000 then the participants are examined in 2010)

cohort

Rare disease Cases usually from hospitals. Matching by age, sex, etc.

case control

Strengths of cohort studies:

• It is a very good design to study a relationship between an exposure and a disease

• Temporality can be established

• Multiple exposures can be studied at the same time

• It enables measurement of incidence rate and cumulative incidence

• It enables measurement of risk as:

a- Relative risk (RR) b- Attributable Risk (risk difference, AR) c- AR exposed % d- AR population %

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• It is a very good design to study a relationship between an exposure and a disease

• Temporality can be established

• Multiple exposures can be studied at the same time

what study?

cohorrt

It enables measurement of incidence rate and cumulative incidence

cohort

• It enables measurement of risk as:

a- Relative risk (RR) b- Attributable Risk (risk difference, AR) c- AR exposed % d- AR population %

cohort

Limitations of cohort studies:

• Loss of follow up

• Costly studies

• More time consuming

• e Confounding is possibl

• Selection bias is possible

• Information bias

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what kind of bias in cohort?

• Selection bias is possible

• Information bias

Confounding is possible in cohort?

yes

• Loss of follow up

• Costly studies

in cohort

Information bias is possible eg. outcome assessment bias.

To avoid bias: it is important that determination of presence or absence of disease be made in a uniform manner for exposed and non exposed cohort members. Accordingly, diagnostic criteria should be established before study begins and should be applied similarly for exposed and non- exposed.

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