# Picking a test confusion

• Aug 20th 2010, 11:43 PM
Daniiel
Picking a test confusion
I have this chemistry stat question.
It has like a story to it, but the bottom line is, theres a guy who had broken glass in his coat, they analyzed what the glass was made up of and compared it to that of the composition of the glass at a crime scene. They want to prove the glass at the crime scene is the same as the glass in his coat with 99% confidence.

It gives the following information
I thought chi square, then i saw they gave the SD so then i thought, i'll just prove them individually untill i find one that isnt 99% true, or till i find they're all 99% confident, but i don't think thats right.
http://img841.imageshack.us/img841/4537/afaf.jpg
Is there a way i can combine all this data, or test that im forgetting to us?
They're all from different distributions so its got me confused.
• Aug 26th 2010, 03:06 AM
CaptainBlack
Quote:

Originally Posted by Daniiel
I have this chemistry stat question.
It has like a story to it, but the bottom line is, theres a guy who had broken glass in his coat, they analyzed what the glass was made up of and compared it to that of the composition of the glass at a crime scene. They want to prove the glass at the crime scene is the same as the glass in his coat with 99% confidence.

It gives the following information
I thought chi square, then i saw they gave the SD so then i thought, i'll just prove them individually untill i find one that isnt 99% true, or till i find they're all 99% confident, but i don't think thats right.
http://img841.imageshack.us/img841/4537/afaf.jpg
Is there a way i can combine all this data, or test that im forgetting to us?
They're all from different distributions so its got me confused.
$\displaystyle z=\dfrac{\left[\frac{C_{As}-W_{As}}{\sqrt{2}s_{As}}+\frac{C_{Co}-W_{Co}}{\sqrt{2}s_{Co}}+\frac{C_{La}-W_{La}}{\sqrt{2}s_{La}}+\frac{C_{Sb}-W_{Sb}}{\sqrt{2}s_{Sb}}+\frac{C_{Th}-W_{Th}}{s_{Th}}\right]}{\sqrt{5}}$
where the $\displaystyle $$Cs are the concentrations in the coat sample and \displaystyle$$ W$s are the concentrations from the window sample, and the $\displaystyle $$ss the corresponding SD of the test results (note the SD of the difference is now \displaystyle \sqrt{2}s which is where the \displaystyle \sqrt{2} terms come from. Now \displaystyle$$ z$ is a standard normal RV and can be tested appropriatly.