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# 如何計算population mean和variance

The following table gives observed

monthly returns for the two stocks:

Month Stock 1 Stock 2

Jan 0.01 -0.02

Feb 0.05 -0.10

Mar -0.02 0.04

Apr 0.02 -0.04

May -0.03 0.06

Jun 0.01 -0.02

Jul 0.01 -0.02

Aug 0.04 -0.08

Sep 0.00 0.00

Oct 0.02 -0.04

Nov -0.04 0.08

Dec -0.02 0.04

(a) What are the values of population mean 1 and population mean 2?

(b) What are the values of population variance 1 and population variance2?

### 1 Answer

- 1 decade agoFavorite Answer
Population mean is the sum of the data divided by the number of population observations.

the formula is: u=(X1+X2+...XN)/ N

Variance is the sum of the squared differences between each observation and the population mean divided by the population size, N.

A.) you sum up the numbers of each stock1 and stock2 individually, and then divided by 12 since the total observations are 12.

so for population mean 1, the calculation is: [0.01+0.05+(-0.02)+...+(-0.02)] / 12

do the same for mean 2.

B.) for population variance 1, you do the following: [(0.01-mean1)^2 +(0.05-mean1)^2 + (-0.02-mean1)^2 +.... +(-0.02-mean1)^2] / 12.

the final answer will be the population variance1.

then you do the same for the variance2.

Source(s): me and my textbook: Statistics for business and economics- Login to reply the answers