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community sheet # 2 of Dr farouq  Yasmine Nofal
JU.De :: 3rd year :: Sheets and slides :: Biostatistics
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community sheet # 2 of Dr farouq  Yasmine Nofal
بسم الله الرحمن الرحيم
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Last lecture we talked about epidemiology which is studying the distribution and determinant of disease of human population .
Distribution of disease includes:
1person :different personal characteristics.
2place: place of occupation while he is working,place of residency.
3 time: long term variation (secular trend): which means variation of a disease or term over a long period of time one of the best examples is the temprophase recorder?? Over the last 50 years going down from 161 to 13..
short term variation (epidemic variation) :which means the temporary of morbidity or mortality over short period of time.
cyclic variation: increase in number of cases of specific disease every specific period of time then goes down ..
Here the Dr shows us a diagram of measles in Jordan starting from 1978 to 1991,,showing the three types of variation..
*Is the factor causes the disease or not ?
Does smoking causes lung cancer ?
To be able to say that smoking causes lung cancer we have to go back to something called criteria of causation (they are 9 criteria) :
1type of study..we'll talk about it next week.
2strength of association..again we'll talk it next week.
3dose response relationship..ex,the relationship between rate of smoking and incidence rate of lung cancer ,,more of cigarette you expect high incidence of lung cancer measured by odds ratio and relative risks.
4temprolity: means the risk factor should become before the onset of disease ex..the person should smoke before you can say that smoking causes lung cancer in that person.
5 consistency:: means the results of your study must be similar to the results of other studies that have carried out at different parts of the world..ex,if you say that extra sugar consumption causes dental caries we should see many studies all of them saying that extra sugar consumption causes dental caries.
*what is the difference between incidence and prevalence rate of the disease? Usually incidence is less than prevalence..
This introduces us to what we call it risk, risk is the probability of having a bad outcome or the probability of getting a disease or die due to action or a disease leads to mortality or morbidity..
we can measure risk by:
1.absolute measure of risk = incidence rate, prevalence rate, attack rate of a disease.
2. odds ratio (OR) or relative risk (RR).
3.attributable risk percentage (AR).
4. wider measure of risk ..(R) value..regression coefficient or correlation coefficient.
we can say that the incidence rate of a disease in sample is 5 then the risk is 5%..
*the Dr showed us a diagram of viral hepatitis over 1 year period
the cases that started before the onset of the year is called old case .
cases that started during the year are called new cases.
 prevalence rate of a disease
K is constant =100%
incidence rate of a disease
prevalence almost =incidence * duration of illness
for example if we have a highly fatal disease like rabies its fatal in a short period of illness, so in rabies incidence is almost equal to prevalence, same applied to common cold which has short period of illness (34 days)
in all diseases prevalence is either more or equal to incidence.
*we have a table 2*2 has 4 cells ,,
+ve cells : exposed to risk factor.
_ve cells: nonexposed to risk factor.
from this table you can calculate the attributable risk percentage
2nd lecture of Dr.Farouq
Yasmine N ofal
JU.De :: 3rd year :: Sheets and slides :: Biostatistics
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