Epidemiology module of practical skills for mbbs student

Calculate mean, mode, and median for hemoglobin values of 20 pregnant women.

12, 10, 8, 9, 12, 10, 7, 9, 7, 10, 11, 8, 12, 7, 8, 13, 11, 9, 10, 11, 7

Mean:

Median:

Mode:

4. 
   MEASURES OF DISPERSION
   

(a) Percentile: Sometime one has to locate other points in the range. This can be done with the help of percentile. Just as the median divides the subjects in two equal groups each with nearly n/2 subjects, the percentiles divide the subjects in 100 equal parts. Each part is containing n/100 subjects. If n= 400, each part will have 4 subjects. The parts are identified by 99 cut points of the measurements under consideration. Consider weight to nearest Kg. of 2 yr old 35 boys:

10, 12, 9, 11, 10, 12, 12, 13, 8, 9 13, 14, 13, 8, 9, 11, 11, 10, 12, 13, 9, 12, 10, 11, 14, 9, 12, 12, 13, 12, 9 13, 10, 11, 10,

For example 20ths percentile of weight is that value below which are 20% children, for n=35, then 20% of children mean 7 children. The procedure is to arrange their weights in ascending order and pick up the seventh value. When arranged in ascending order, there weights in Kg. are:

8, 8, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 12, 12, 12, 13, 12, 12, 12, 13, 13, 13, 13, 13, 13, 13, 14, 14

The seventh value is 9 kg. This is the 20^th percentile of weight of 2 yr old boys as far as these data are concerned. Similarly we can find out given percentile by adopting the above procedure. It can be determined by the formula [kth percentile = (k X n/100)].