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# S3 Coursework Question watch

1. Hi, im a bit stuck.

I am doing a 1-tailed diference of 2 mean's test, i have taken a 2 samples from thier populations ( i also have all the population data),

My query is that what is the variance i should use in the test calculations? the hieneman edexcel s3 book seems to indicate that you use the population variance? but a m8 says its the variance from the sample data that i should take. (why does only 1 other person in my school take further maths lol !!)

The s3 book seems to be no help in this matter, somebody who knows pls help me, tell me which variance to take and which formula for the variance i should use.

To anybody who replies thank you very much for your time.
2. Well you can't use the population variance, since you don't know it

What you do is to work out the estimate of the population variance from the sample = s^2 = (Sum(x^2) - n(Sum(x)/n)^2)/(n-1). You may say if n is significantly large, then s is approximately sigma, so you use s in your difference of two means test.
3. Thanks loads theone , that helps me a lot lol, now i can finish that hypothesis! yay

Only 1 more hypothesis to go! better finishthis thing soon
4. (Original post by Kabeer)
Thanks loads theone , that helps me a lot lol, now i can finish that hypothesis! yay

Only 1 more hypothesis to go! better finishthis thing soon
No problem, well done!

I finished my hypotheses yesterday in one big session of S3 coursework Just got data collection and summary to finish and i'll be done.
5. (Original post by theone)
No problem, well done!

I finished my hypotheses yesterday in one big session of S3 coursework Just got data collection and summary to finish and i'll be done.
theone, how are you finding STEP? Is it rock hard or ok?
6. (Original post by bono_3)
theone, how are you finding STEP? Is it rock hard or ok?
Tis fine mostly, of course there are several hard questions, it's just picking the ones I can do. practice is of course invaluable (See the stress of STEP thread in Oxbridge section).

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