‫بسم هللا الرحمن الرحیم‬
‫اندازه گیری در اپیدمیولوژی‬
‫‪Epidemiologic Measures‬‬
‫دکتر حسین صافی زاده‬
‫بهمن ‪1389‬‬
‫منبع ‪:‬درسنامه طب پیشگیری و پزشکی اجتماعی پارک جلد اول ‪،‬فصل اول‬
‫اهداف درس‬
‫انتظار می رود شما با مطالعه این درس‪:‬‬
‫‪ ‬اصطالحات نسبت‪ ،‬تناسب و میزان را توضیح دهد‪.‬‬
‫‪ ‬مفهوم صورت و مخرج کسر را در مورد میزان توضیح دهد‪.‬‬
‫‪ ‬اندازه گیری های مربوط به مرگ و میر را توضیح دهد‪.‬‬
‫‪ ‬اندازه گیری های مربوط به مرگ و میر را محاسبه نماید‪.‬‬
‫‪ ‬اندازه گیری های مربوط به ابتال را توضیح دهد‪.‬‬
‫‪ ‬رابطه بین بروز و شیوع را توضیح دهد‪.‬‬
‫‪ ‬اندازه گیری های مربوط به ابتال را محاسبه نماید‪.‬‬
‫‪Epidemiologic Measures‬‬
‫•‬
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‫•‬
‫•‬
‫•‬
‫•‬
‫•‬
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‫اندازه گیری میزان مرگ و میر (‪)Mortality‬‬
‫اندازه گیری ابتال به بیماری ها (‪)Morbidity‬‬
‫اندازه گیری معلولیت و ناتوانی (‪)Disability & Handicap‬‬
‫اندازه گیری موالید (‪)Birth‬‬
‫اندازه گیری حضور‪ ،‬فقدان و یا چگونگی توزیع خصوصیات یا‬
‫صفات مربوط به بیماری ها‬
‫اندازه گیری نیازهای پزشکی‪ ،‬تسهیالت بهداشتی‪ ،‬استفاده از خدمات‬
‫بهداشتی‬
‫اندازه گیری‪ ،‬حضور‪ ،‬فقدان و یا توزیع عوامل محیطی و یا سایر‬
‫عواملی که ممکن است نقش علیتی برای ایجاد بیماری داشته باشند‪.‬‬
‫اندازه گیری متغیرهای جمعیتی‬
‫فرض کنید در یک مدرسه شبانه روزی‬
‫‪ 10‬دانش آموز دچار آنفلوانزا شده باشند‪.‬‬
‫به نظر شما وسعت مشکل دراین مدرسه چقدر می باشد؟‬
‫آیا دانستن تعداد بیماران به تنهایی کافی می باشد؟‬
‫برای درک بهتر حجم مشکل‪ ،‬به چه اطالعاتی نیاز می باشد؟‬
‫‪N = 50‬‬
N = 240
N = 240
N = 50
Epidemiologic Measures
)Ratio( ‫• نسبت‬
)Proportion( ‫• تناسب‬
)Rate( ‫• میزان‬
Ratio
‫نسبت‬
• Used to compare two quantities
Examples:
 Ratio of male to female birth
Male
8

Female 4
Ratio
‫نسبت‬
Examples:
 Ratio of physician to population
Physician
1

Population 5000
Ratio
‫نسبت‬
Examples:
 Ratio of WBC to RBC
WBC
1

RBC
600
‫نسبت‬
‫‪Ratio‬‬
‫• از ابزارهای اندازه گیری فراوانی بیماری ها می باشد‪.‬‬
‫• صورت کسر‪ ،‬بخشی از مخرج کسر نیست‪.‬‬
‫• صورت و مخرج کسر ممکن است‪ ،‬فاصله زمانی‬
‫داشته و یا هر دو لحظه ای بیان شوند‪.‬‬
Proportion
‫تناسب‬
Proportion
‫تناسب‬
Proportion
‫تناسب‬
• A specific type of ratio in which the
numerator is included in the denominator
• Usually presented as a percentage
A
 100
A B
Proportion
‫تناسب‬
5
 100
20
• Tell us what fraction of population is affected
Proportion
‫تناسب‬
Example:
Male undergoing bypass surgery at hospital A
Total patients undergoing bypass surgery at hospital A
× 100
‫میزان‬
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‫‪Rate‬‬
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Rate
‫میزان‬
• Special form of proportion that includes
a specification of time
• Most commonly used in epidemiology
because it most clearly expresses
probability or risk of disease or other
events in a defined population over a
specified period of time
Rate
‫میزان‬
• Special form of proportion that includes
a specification of time
• Most commonly used in epidemiology
because it most clearly expresses
probability or risk of disease or other
events in a defined population over a
specified period of time
Rate
‫میزان‬
Tell us how fast the
disease
is
occurring
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in a population
Defined Population
Specified period of time
Rate
‫میزان‬
Number of events in a specified time period
×K
Population at risk of these events in a specified time period
 K is used to denote the units of population such as per
1000 or per 100,000
3200 deaths in kerman in 1388
800,000 Population in kerman in 1388
× 1000 = 4 per 1000
Numerator & Denominator
• Numerator is number of events that occurred in a
defined population over a specified period of time
• Denominator
 Population
 Population at midyear
 Population at risk
 Person-time
 Person-distance
 Subgroups in population
 Events
Epidemiologic Measures
• Measurement of Mortality
• Measurement of Morbidity
Measurement of Mortality
 Crude death rate
Total no. of deaths from all causes in 1 year
No. of persons in the population at midyear
× 1000
Measurement of Mortality
 Crude death rate
Total no. of deaths from all causes in 1 year
No. of persons in the population at midyear
× 1000
Example :
3200 deaths in 800,000 Population
CDR= 3200/800,000 × 1000 = 4 per 1000
Measurement of Mortality
 Specific mortality rates
 Age-specific mortality rate
No. of deaths from all causes in 1 year in children younger than 5 years
× 1000
No. of children in the population younger than 5 years
Measurement of Mortality
 Specific mortality rates
 Age-specific mortality rate
No. of deaths from all causes in 1 year in children younger than 5 years
× 1000
No. of children in the population younger than 5 years
Measurement of Mortality
 Specific mortality rates
 Cause (disease) –specific mortality rate
No. of deaths from lung cancer in 1 year
× 1000
No. of persons in the population at midyear
Measurement of Mortality
 Specific mortality rates
 Age-specific mortality rate
 Cause (disease) –specific mortality rate
No. of deaths from leukemia in 1 year in children younger than 10 years
× 1000
No. of children in the population children younger than 10 years
Measurement of Mortality
Example :
Population A
Population B
CDR= 15.2 per 1000
CDR= 9.9 per 1000
What population have better condition?
Measurement of Mortality
Age – specific mortality rate in 1000 persons
CDR
<1
A
15.2 13.5
B
9.9
22.6
1 - 4 5 - 7 8 - 44 45 - 64 > 65
0.6
0.4
1.5
10.7
59.7
1
0.5
3.6
18.8
61.1
Measurement of Mortality
 Case – fatality rate
No. of individuals dying during a specified
period of time after disease onset or diagnosis
× 100
No. of individuals with the specified disease
 Proportionate mortality Rate
- Of all deaths, what proportion were due to disease “ X ”
No. of deaths from IHD in the kerman in 1388
× 100
Total deaths in the kerman in 1388
Measurement of Mortality
 Survival rate
- Five – years survival : The percent of patients who are
alive 5 years after treatment begins or 5 years after
diagnosis
Measurement of Morbidity
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New case
Incidence
Incidence
‫بروز‬
The number of new cases of disease that occur
during a specified period of time in a population
at risk for developing the disease
Measure of the probability that unaffected
persons will develop the disease
Steps:
 identify a population that is free of the disease
 follow the population over time
• Observe person-time
 record new cases of disease as they occur
Incidence
‫بروز‬
Formula:
No. of new cases of a disease occurring in the
population during a specified period of time
No. of persons at risk of developing the disease
During that period of time
× 1000
Example:
70 new cases of breast cancer in a 5 years period
× 1000 = 23
3000 women at risk
( 23 Cases per 1000 women during 5 years )
Measurement of Morbidity
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Prevalence
Prevalence
‫شیوع‬
The number of affected persons present in the
population at a specific time divided by the number
of persons in the population at that time
Provides estimate of the probability or risk at one
will be ill at a point in the time
Provides an idea of how severe a problem may be
Useful for planning health services (facilities, staff)
‫شیوع‬
Prevalence
Formula:
No. of cases of a disease present in the
population at a specified time
× 1000
No. of persons in the population at that specified time
Example:
700 cases of HTN in 1388
× 1000 = 2.3
300,000
( 2.3 Cases per 1000 persons )
Prevalence
‫شیوع‬
Type of Prevalence :
1) Point prevalence


Prevalence of disease at a point in time
Number of cases that exist at a given point in time
2) Period prevalence

Number of cases that exist in a population at any time during a
certain period
Prevalence & Incidence

Prevalence varies directly with:


Incidence
Duration of disease
 If incidence is low, but duration is long (chronic);
Prevalence will be large in relation to incidence
 If prevalence is low because of short duration
(due to recovery or death);
Prevalence will be small in relation to incidence
Prevalence = Incidence × Duration
Prevalence Vs. Incidence
Prevalence = Incidence X Duration
P=IXD
Prevalence Vs. Incidence
Prevalence
?
Exercise
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Exercise
1388
?
Incidence
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‫خسته نباشید!‬
‫موج نهم ـــ اثر‪ :‬ایوان آیوازوفسکی ‪ 1850‬ـــ محل نگهداری‪ :‬موزه دولتی روسیه‪ ،‬سن پترزبورگ‬