The last deviation can be found as the mean of the deviations from the meanOriginally Posted by skhan
is zeros. So let be the missing deviation, then:
so
.
Now the variance:
where the s are the deviations from the mean, so:
RonL
A student wants to calculate the variance of a set of 10 scores. Unfortunately, he doesn't have the raw scores but only has the deviation of each raw score from the mean. Worse yet, he only has 9 of these deviation scores, as listed below. Compute the variance for him.
-5, +11, -4, -2, +7, -8, -6, +1, -3
I have no idea how to do this problem
The last deviation can be found as the mean of the deviations from the meanOriginally Posted by skhan
is zeros. So let be the missing deviation, then:
so
.
Now the variance:
where the s are the deviations from the mean, so:
RonL
Originally Posted by skhan
That is because this given answer is using the unbiased population variance
estimator which is:
.
which in this case is .
(Now I would argue that this is the wrong answer to the problem as asked,
which was what is the variance of the given set of deviations, but what
are you gonna do?)
RonL
I see what you are saying.Originally Posted by CaptainBlack
But it should be,
squared-mean minus mean-squared.
The easy way to remember is the the word "mean" means middle. Thus, it needs to be in the middle of the sentence.
I use this mnemonic because last year in Math B class the students very insane about the variance formula and the math teacher said people have to memorize it. This is what some of them learned.
This is my 12th Post!!!