•Why should we be concerned with monitoring disease(s)?
•Disease Control and Prevention
Good monitoring does not necessarily
ensure the making of right decisions,
but it reduces the risk of wrong ones.
•There are several decisions regarding Disease monitoring
•What level of resources should be allocated to disease monitoring?
•What outcomes do we want to achieve?
•What benefits are obtained from these items and to whom do the benefits accrue?
•Can the counting methods be readily accepted into the community?
•Approaches Towards Monitoring Disease and Injury
•Systematic, regular ascertainment of incidence using methods distinguished by their practicality, uniformity, and frequently their rapidity, rather than by complete accuracy
Let’s spend some more time talking about each of the major systems for identifying injuries. The primary means to identify injuries is to establish a surveillance system.
What is a surveillance system? John Last has defined surveillance as the regular assessment of disease or injuries, with a common method, and often an approach that is simplistic rather than complex. One of the key words here is regular assessment. Injury monitoring, such as that with death certificates, is set up to evaluate injuries over time. With common methods, this allows a researcher to examine changes over time in these events..
•Types of Surveillance
•the collection of data on a disease by regular outreach. Designated medical personnel are called at regular intervals to collect information on the new cases of disease
Active surveillance involves the regular monitoring of surveillance sites by designated persons. These persons often call up a site to gather information on injury events that happened in the previous month or week. One example of this process would be the surveillance of injuries from domestic violence in emergency departments. Research personnel would contact emergency departments on a regular interval to identify injury events from domestic violence. As no data sources routinely identify domestic violence injuries, this type of active surveillance is necessary to identify the incidence of domestic violence events..
•data generated without contact by the agency carrying out the surveillance. Reportable diseases fall under this type of surveillance
More commonly surveillance systems are passive. By definition, researchers or health department personnel do not go out into the community to find cases. Rather, they develop instruments that persons in the community have to send into them (e.g. death certificates) as a means of identifying events. Reportable diseases such as AIDS and malaria, etc. are monitored in this fashion.
Laboratories, physicians, and hospitals have to report these events to the health department when they identify a case at their institution.
In some states, spinal cord injuries are a reportable condition and are followed with passive surveillance..
•So you have identified the Frequency of disease in a given area….
•What do you do with it?
•Epidemiology is a Science of Rates
Epidemiology is a science based upon rates. Incidence and prevalence rates provide information on the importance of a disease or injury in a defined population. Understanding how many injuries occur (the absolute number) provides only one part of the puzzle; the numerator. The second piece is the population in which they occur; the denominator. As we will see, the denominator is a very important factor in defining the significance of a problem.
Effective injury control is based upon an understanding of injury rates; i.e. how many injuries occur within a given population.
مشكوووره الاخت كفاااح بصراحة معلومات قيمة
بس ودي تنزلي مقال عن rates and ration في المراكز الرعاية والمستشفيات
Rates, Ratio and Proportions
•Rates, Ratio and Proportions
A ratio is made of 2 elements, the numerator “a” and the denominator “b”.
عددالمواليد الذكور\ عدد المواليد الإناث
•A proportion is a ratio where the numerator “a” is part of the
•عددالمواليد الذكور\ عددالمواليد الذكور+عدد المواليد الاناث
•Rate is a proportion that is specified in time, thus a rate for disease would be
Measures of Mortality
•Indices of Mortality
Crude Death Rates =
# death in during the year\
Death Rates =
# death due to spc disease\
Population at risk
Death Rates =
# death among persons in a given age group\
Population size in given age group
Case Fatality Rate =
# death due to spc disease\
Total number of people with disease
# death due to spc disease\
Total number of death from all diseases
Maternal Mortality Rate=
# death due to puerperal causes\
Total number of live births
•Measures of Morbidity
•Indices of Morbidity
Incidence Rate =
# NEW cases of disease\
population at Risk of disease
يضرب الناتج في
Over a period of time
Prevalence Rate =
EXISITING cases of disease\
At a given point in time
Indices of Morbidity
•More on Incident and Prevalent Cases
•Incident cases are the new cases that emerges in a defined population during a specific period of time
•Prevalent cases are cases that were present for all or part of a specific period of time:
Point prevalence: The period of time is short Period prevalence: the period of time is longer
•Measures of Fertility
•Indices of fertility
Crude Birth Rate =
# live births\Total Population
Indices of fertility
General Fertility Rate=
# live births\
Total # of women in childbearing age
•Adjusting Death Rates
•The need for Adjusted Rates
•When comparing the crude death rates between Panama and Sweden, one would expect that Sweden would have lower crude death Rates.
•However the numbers show a reverse pattern where Panama CDR = 9.37 per 1000 and
Sweden CDR = 10.20 per 1000
•Lets look at the age distribution
•The Age Pyramid
•It is clear that Sweden has a larger % of its population in the older group.
•And we know that the age specific death rates of older people is higher than the younger one.
•From the previous tables it is clear that:
•The Age distribution between the 2 countries is different
•Within each age group, the Age Spc DR for Panama is higher
•Nonetheless the CDR for panama is lower
•Thus we need to account for the age distribution: Adjust for Age
•There are 2 ways to adjust for age:
•The Direct Method
•The Indirect Method
•The Direct Method requires the knowledge of the Age SDR for each country
•Then a Standard Age Distribution is selected, and applied to Both
•Direct Method of Adjustment
•Lets suppose the age distribution of Panama was the same as Sweden. Meaning we will select the age distribution of Sweden as the standard one
•Then we apply to Age SDR using the new distribution, get the total number of deaths, and then calculate the Adjusted DR
•Direct Method of Adjustment
•Sweden CDR = 10.2
•Panama CDR = 9.37
•After Adjustment the new A
Adjusted DR = 13.1
•Clearly the Death Rate in Panama is higher
•Indirect Method of Adjustment
•As we said earlier, the indirect method is used when the age specific death rates is not known.
•Let’s suppose we did not know the Age Specific death rates for Panama.
•Then we would used the age specific death rates of Sweden for panama, and get the expected numbers of Death
•Survival and Life Expectancy
•In the following example we will show how the Expected life expectancy is calculated
•The life table shows the life expectancy at each age interval
•Lets do the example on Excel
•Sources of Data
•Source of data
•There are different sources of data on mortality and morbidity in the community.
•Each source bear its advantage and disadvantages.
4.Linked health records
•Is the periodic counts or enumeration of a population.
In the states every 10 years there is a complete census.
Census assess a wide range of factors: age ***, marital status, race….
The information available in census help to quantify the number of people living in an area, or a subgroup such as woman, elderly, infants…
This information is essential in calculating rate, and other mortality and morbidity statistics
•Ongoing recording of the vital events of a population: birth, death, marriage, divorce.
The important one for Epi are death, featal death and birth.
1. Death Certificates: provides info on the dead person such as age *** race occupation, also can be used to quantify frequency of death. It also provide cause of death, used for calculating specific death rates (how else would we know the leading cause of death).
The physician must assign a cause of death from a list of tabulated codes in the ICD (Injuries and Causes of Death).
2. Certificate of Live Birth: information provide: ***, weight at birth, mother and father age, gestational age, parents education, congenital abnormalities, previous pregnancies…..
3. Certificate of Fetal Death: definition by WHO is all fetal death regardless of gestational age, nonetheless the practice in the states not to record unless it has 20 weeks of gestational age (almost 4 months)
•There are organizations that deals with collecting information of occurrence of specific disease. One major organization in the states is the CDC (Center for Disease Control and Prevention).
1. Notifiable disease: Depending on countries there are a list of disease that are required to be reported to the officials, the idea is to keep track of the prevalence of disease to make sure if an epidemic occur to be able to stop it as quickly as possible. Also some disease are dangerous and contagious. (through reporting the States were able to figure out about the Anthrax, Mad Cow disease, AIDS)
•4 disease are required to be reported internationally: Cholera, Plague, Smallpox, and Yellow fever.
many countries report cases of cancer and AIDS.
2. Hospital records: are also rich with data
3. Private Clinics
4. Disease registries.
5. Special surveys: National health surveys includes the Health Interview survey, Health and Nutrition examination survey,
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