wt is standard deviation..and inter quartile ranga???

The standard deviation(標準差) is the most common measure of statistical dispersion, measuring how widely spread the values in a data set are. If the data points are close to the mean, then the standard deviation is small. Conversely, if many data points are far from the mean, then the standard deviation is large.

Sample s.d. example:
suppose you have a set of data {1,2,3,4}
first, you calculate the sample mean=(1+2+3+4)/4=2.5
then find the variance=(1/n)*[(x1-2.5)^2+(x2-2.5)^2+(x3-2.5)^2+(x4-2.5)^2]
=(1/4)*[(1-2.5)^2+(2-2.5)^2+(3-2.5)^2+(4-2.5)^2]=5/4=1.25
standard deviation is the square root of variance=sqrt(1.25)=1.118

Population s.d. example:
assume the population follows binomial with n, p given,
expected value=np
variance=np(1-p)
s.d=sqrt[np(1-p)]

Interquartile range (IQR) is the range between the third and first quartiles and is a measure of statistical dispersion (Q3-Q1 or 75% percentile - 25% percentile of the distribution)

IQR calculation:
say you are given a set of data,
you first arrange it from small to large,
then you divide the data into 4 equal parts,
use the number divided the 3rd and 4th part subtract the number divided the 1st and 2nd part,
the number you get will be the IQR.