Board 8 > Any experts in Statistics here?

(+) Yeah! (+)

I don't know the formulas off the top of my head or whatever but try dividing the stddev by sqrt(n) or something. Basically find the standard ERROR not the standard DEVIATION.

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senorhousemouse

I'm prepping for an exam and I can't seem to figure out how to calculate the P-value when you're comparing two samples in Difference Between Two Means and Comparing the Means of Two Related Populations.

I can find the t statistic and confidence intervals fine but one of the practice questions asks for the P-value. And whenever I look up how they do it in the book, they say they plugged it into Excel which we can't use... so I look back to how they original calculate it and they find the z-stat first. But finding that requires: x-mu / stan dev or xbar - mu / stan dev / sqrt(n)

I only have sample data and not population mean or population standard deviation. I tried estimating it using the sample numbers but I'm not getting the same answer as the book gives. Help?

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Menji - Sign My Petition for "Search By Username"
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Oh Boy. I came in 12th in the state in stat but that was Years ago.


If you only have the sample data and not the population data I don't think you even can find the one you are looking for. Doesn't one test go with Population and another for sample size? Are you sure you need the P value then? Are you sure you need to know that for your exam?

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yE frE me Kweku Ananse Papa
me:http://img235.imageshack.us/img235/1508/masterplumgm3.jpg

Well it's one of the questions he said to practice.

Let me explain this more in depth. I'm comparing the means of two related populations:

Seven patients, we have their before and after data numbers for their blood.
1 - 158 - 284
2 - 189 - 214
3 - 202 - 101
4 - 353 - 227
5 - 416 - 290
6 - 426 - 176
7 - 441 - 290

The first part was at .05 significance, is there evidence that the mean is higher before than after the transplant. I did not reject the Ho because my tstat was 1.84 which was < 1.94 from DoF = n-1 at .05

Then they ask for the p-value which the back of the book gives as 0.0575. I have no idea how they get this.

Also, I might be confusing my variables. sigma = sample st dev and s = pop st dev, correct? I just don't know what to use for mu in the Z stat equation since I don't have that.

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Menji+ What Will Never Be the Greatest.
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oh and I am using stand dev variables backward

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Menji - www.last.fm/user/menjii
You got to put me on. Come on! Come on!

maybe but its probably been too long

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~Wigs~
New York FOOTBALL Giants: SUPER BOWL XLVI CHAMPIONS

From: Menji76 | Posted: 3/5/2012 7:34:26 PM | #004
Also, I might be confusing my variables. sigma = sample st dev and s = pop st dev, correct?

this is backwards I believe

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~Wigs~
New York FOOTBALL Giants: SUPER BOWL XLVI CHAMPIONS

too slow wigs

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Menji
"I'm on a f***ing bicycle ding ding ding."

I think you have to reverse the table, basically. Find what significance corresponds to the t-value you got. You probably have to interpolate.

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No amount of planning will ever replace dumb luck.