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Statistics II Question

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astarmathsandphysics:
It is because in the variance (x-mean) is squared so if you double x, you double the mean and get(2x-2*mean)^2 which is 2^2(x-mean)^2

Superstrings:
When a co-efficient is given for any variables, then it's always squared.


The problem is that the examiner may not be nice, and you have to form the equation yourself, in which case, things can go something like

X + X + X + X + X + Y + Y + Y

or

5X + 3Y.

This generally causes a lot of confusion.

In this case, coin toss =/= poisson so mean =/= variance.
Therefore you can't just find the mean and assume it's the same as the variance.

I think your question is, "To square or not to square, the variance co-efficient?"

Well, there is no straightforward answer.
Let's say, there is a long jumper, whose distances have a mean of 5m and s.d. of 0.5m.
No two jumps will ever be the same... (although they can be the same distance)
If you have currency, $50 will always = $50, so it is squared.

I'm sorry I haven't been more clear, but in time, you will be used to it.
I'll stick around this topic ^^

vince_24:

--- Quote from: Superstrings on November 08, 2009, 07:50:17 am ---When a co-efficient is given for any variables, then it's always squared.


The problem is that the examiner may not be nice, and you have to form the equation yourself, in which case, things can go something like

X + X + X + X + X + Y + Y + Y

or

5X + 3Y.

This generally causes a lot of confusion.

In this case, coin toss =/= poisson so mean =/= variance.
Therefore you can't just find the mean and assume it's the same as the variance.

I think your question is, "To square or not to square, the variance co-efficient?"

Well, there is no straightforward answer.
Let's say, there is a long jumper, whose distances have a mean of 5m and s.d. of 0.5m.
No two jumps will ever be the same... (although they can be the same distance)
If you have currency, $50 will always = $50, so it is squared.

I'm sorry I haven't been more clear, but in time, you will be used to it.
I'll stick around this topic ^^

--- End quote ---

Thanks for the help. For the coin question, the mark scheme states you have to square the co-efficient of the variance, thus giving the mean = 5 and variance = 5.

You are getting to my question, if it isnt too much trouble, could you give a further example? Thanks for your time.

astarmathsandphysics:
If the average price of petrol triples the variance will be multiplied by 3^2. Noticed the standard deviation is only multiplied by 3 cos it is sqrt(variance)

Superstrings:
For the coin question the variance is squared. This is because you are repeating the same test.

If you found this information useful, please mail max g's to
Iksa
Thaurissan
Alliance


Thanks :p

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