Epidemiology module of practical skills for mbbs student

(b) Deciles, Quartiles and Tertiles:

Deciles divide the group of subject in to 10 equal parts. Quartiles in to four equal parts and tertiles into three equal parts. Tertiles are often used to divide the subjects into those with low, medium and high values.

4. 
   MEASUREMENTS OF MORBIDITY
   

Morbidity data should be accurately and completely collected and transformed into various rates to make the understanding of magnitude of the health related event meaningful.

1. 
   Incidence Rate (IR):
   

It is the number of new events that occurs in a defined time period in a geographical area. The denominator is the population at risk for that event during that period. The most accurate way of calculating incidence rate is person-time incidence rate. Each person in the study population contributes one-person year to the denominator for each year of observations before disease develops or the person is lost to follow-up.

No. of people who get a disease in a specified period

IR =______________________________________________X 1000

Sum of the length of time during which each person in the

population is at risk.

The incidence rate takes into account the variable time periods during which individuals are disease free and thus at risk of developing the disease. Since it may not be possible to measure disease free periods precisely, the denominator is often calculated approximately by multiplying the average size of the study population by the length of the study period. This is reasonably accurate if the size of the population is stable and I.R. is low. For example, in a sub-center with population of 5000 there are 5 new cases of tuberculosis occurred during one year. For this disease the whole population is at risk of tuberculosis, hence the incidence rate of tuberculosis would be 1 per 1000.

EXERCISE

In order to measure the quantum of sickness in children under 5 years of age , a astudy was conducted among 153 children from May 2004 to April 2005 in Urban area . The five leading cause of illness of number of person ill and spels of illness is as follows ;

Disease	No of children ill	No. of spell
Common cold	103	169
Diarrhea	62	132
Boils	60	73
Fever	37	42
Conjuctivities	31	37

Calculate

1. 
   Incidence rate(person) for each of the leading cause?
   
2. 
   Incidence rates (spells) for each of the leading cuses?
   
3. 
   Spells of illness for each disease for each sick child?