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To

presentation

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Indicators of health Epidemiology

Mortality indicator Morbidity indicator

Measures

persons who are ill

(No.of people)

Illness

OrIllnesses

Duration of

illness or illnesses

Morbidity rate

Disease Frequency Disease Duration Disease Severity

By Mac Mohan:

(1960)

The study of the

distribution &

determinantsof

disease frequency

in man.

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Incidence rate Prevalence rate

No. of new cases occurring

in the defined population

during specified period of time.

It refers to No. of current cases

Current cases means blend of old

and new cases

At a given point of time

In a specified population

Distribution of

disease

Time

Place

Person

Determinants of

disease

Identifycause

Testing ofintervention

Cause &effect

DESCRIPTIVE EPIDEMIOLOGY ANALYTIC EPIDEMIOLOGY

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EPIDEMIOLOGICAL METHODS

Epidemiological methods

Observational studies

Descriptive

studies

Analytical studies

Experimental studies

RCT Field trial Community trial

Ecological study Cross-sectional study Case control Cohort study

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DEFINITION OF EPIDEMIOLOGY.

By Mac Mohan: (1960)The study of the distribution & determinantsof disease frequency in man.

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RISK.

Risk, or cumulative incidence, is a measure of theoccurrence of new cases of the disease of interest in the

population.

More precisely, risk is the proportion of unaffectedindividuals who, on average, will contract the diseaseof interest over a specified period of time.

Risk, which has no units, lies between 0 (when no newoccurrences arise) and 1 (when, at the other extreme,the entire population becomes affected during the risk

period).

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CALCULATION OF RISK

Number of new cases A

R =--------------------------------------------- = -------

size of the unaffected population N

R- Estimated risk

A- New casesN- size of the unaffected population under

observation

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EXAMPLE-1

A hypothetical study of six subjects illustrates the calculation of risk.

This study began in 1995 and concluded in 2004.

Individual subjects entered the study at various times, were all free of

the disease of interest at the time of enrollment, and were followed up

for at least 2 years.

Patient Awas enrolled in 1995, was diagnosed with the disease just

prior to 1997, and was followed up until death in 2002. Patient Bwas enrolled in 1997, was followed up until 1999 without

developing the disease, and then discontinued participation in the

study.

Patient Cwas enrolled in 1999, was diagnosed with the disease just

prior to 2002, and survived through the end of the observation period

in 2004.

Patients D, E, and F entered the study in 1997, 1998, and 2002

respectively. Each patient was followed through 2004 without

developing the disease.

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CONT..

Of the six subjects under observation (N = 6),

only two (A = 2) developed the disease.

The 9-year risk of disease, therefore,

Estimated R is 0.3 (33%)

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INCIDENCE.

The incidence rate (IR), like risk, reflectsoccurrence of new cases of the disease ofinterest.

Incidence rate measures the rapidity withwhich newly diagnosed cases of the disease of

interest develop over a period of time.

The unit of measuring incidence isCases/person-time

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CALCULATION OF INCIDENCE RATE

No. of new cases of disease of interest A

IR = ----------------------------------------------- = ---

person-time PT

IR - Incidence Rate

A - No. of new cases of disease of interest

PT - person-time

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FROM EXAMPLE-1

Patient A was enrolled in 1995, was diagnosed with the disease just

prior to 1997.(2YRS)

Patient B was enrolled in 1997, was followed up until 1999 without

developing the disease, and then discontinued participation in the

study. (2YRS)

Patient C was enrolled in 1999, was diagnosed with the disease just

prior to 2002, (3YRS)

Patients D, E, and F entered the study in 1997, 1998, and 2002respectively. Each patient was followed through 2004 without

developing the disease. (7YRS) (6YRS) (2YRS) respectively.

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CONT

With above simplification W.K.T

1. A=2

2. PT= 2+2+3+7+6+2=22

3. Therefore, the IR of disease is 0.09

Cases/person-time

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PREVALENCE.

Prevalence indicates the number of existing casesof the disease of interest in a population.

Specifically, the point prevalence (P) is theproportion of a population that has the disease ofinterest at a particular (given point) time.

Prevalence, like risk, ranges between 0 and 1 andhas no units.

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CALCULATION OF PREVALENCE

No. of existing affected individuals C

P = ----------------------------------------- = -------

No. of Persons in the population N

P- Prevalence

C- No. of existing affected individuals

N- No. of Persons in the population

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FROM EXAMPLE-1

Patient A was diagnosed with the disease -2002

Patient B was enrolled then discontinuedparticipation in the study -

1999

Patient C was enrolled was diagnosed with the disease -2004

Patients D, E, and F entered the study Each patient was followed up

to 2004 without developing the disease.

With above simplification to calculate prevalence( at given point of time

considering 2004) W.K.T

1. No. of existing affected individuals C=1

2. No. of Persons in the population N=4

3. Therefore, the prevalence of disease is 0.25 (25%)

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Characteristics of Risk, Prevalence, and

Incidence Rate.

Characteristic Risk Prevalence Incidence Rate

What is

measured ?

Probability of

disease

Percentage of

population with

disease

Rapidity of

disease

occurrence

Units None None Cases/person-

time

Time of diseasediagnosis Newly diagnosed Existing Newly diagnosed

Synonyms Cumulative

incidence

None Incidence

density

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ANNOTATION-1

Risbud A., Mehendale S., Basu S., Kulkarni S., & al, e. (2002). Prevalence

and incidence of hepatitis B virus infection in STD clinic attendees in Pune,

India. Sexually Transmitted Infections, 78(3), 169-73.

The purpose of the study was to estimate the prevalence

and incidence of hepatitis B virus (HBV) infection among patients

attending three STD clinics in Pune, India, and to identify associated risk

factors. The researcher screened 497 out of 2098 Patients at STD clinics

in Pune during 1996, who returned for at least one follow up visit. The

study showed that out Of 497 participants 3.6%, 26.5%, and 43.2% were

positive for HBsAg, anti-HBs, and anti- HBc respectively. This study

concluded that a high prevalence and incidence of HBV infection, seen in

STD clinic attendees, under scored the need to provide HBV vaccine to

commercial sex workers and their clients in India.

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1. Park. K. Textbook of preventive & social medicine21st edition, M/S Banarasidas Bhanot publishers-Jabalpur, India.p.61-64.

2. Stanhope.M, Lancaster J, public health nursing,8thedition, Elsevierpublication, charlottesvilla,virgina.p257-261.

3. Raymond.S.G Medical epidemiology, 4thedition langepublications. p 5-15

REFERENCES.

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