Transcript 2-Measuring
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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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
1389
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
1388
1389
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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1389
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
1388
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
1389
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موج نهم ـــ اثر :ایوان آیوازوفسکی 1850ـــ محل نگهداری :موزه دولتی روسیه ،سن پترزبورگ