Re: Paired difference T-Test

Quote:

Originally Posted by

**thomasboateng**

__but what __**i don't understand** is how they get for the standard deviation s(n-1)=0.8316

I don't know what this figure is, each machine will have its own variance and because this is a paried test there will be a pooled variance to help caclulate the test statistic.

Your null hypothesis will be

$\displaystyle \displaystyle H_0: \mu_B \leq \mu_A \implies \mu_B - \mu_A\leq 0$

so $\displaystyle \displaystyle H_A: \mu_B > \mu_A \implies \mu_B - \mu_A > 0$

After doing this test I found a p-value of 0.71, what does this mean?

Re: Paired difference T-Test

I understand how to get the critical value its 1.833 but i don't get how you get the p value or the standard deviation?

Re: Paired difference T-Test

Quote:

Originally Posted by

**thomasboateng** I understand how to get the critical value its 1.833 but i don't get how you get the p value or the standard deviation?

If you have the critical value you do not need the p-value, what you do need is the value of the test statistic, which you will compare with the critical value.

CB

Re: Paired difference T-Test

i see. the formula for the test statistic is easy enough except for i dont get which steps they used in order to obtain the standard deviation

Re: Paired difference T-Test

question 1) explain 'greater amount' of what

question 2) why is this a paired t-test?

Is it just because the two samples sizes are the same?

That necessary, not sufficient.

Re: Paired difference T-Test

why wouldnt it be. it has the characteristics for a paired diff test. it doesnt matter what it produces thats not the point

Re: Paired difference T-Test

If the two samples are independent then it's not a paired difference experiment.

I do not see enough information go either way.

Re: Paired difference T-Test

Quote:

Originally Posted by

**matheagle** If the two samples are independent then it's not a paired difference experiment.

I do not see enough information go either way.

The machines are at a common temperature which varies from sample period to sample period. The null hypothesis is that the difference between the machine outputs in a period has zero mean. A paired test is appropriate (subject to the other conditions for a t-test being applicable).

CB

Re: Paired difference T-Test

yeah i know that. but standard deviation method?

Re: Paired difference T-Test

Quote:

Originally Posted by

**thomasboateng** yeah i know that. but standard deviation method?

The SD of the differences s_D is computed in the usual way (there is just one sample of differences). Use the population SD estimate formula (that is the one with division by n-1 rather than n). The standard error is required for the test is s_D/sqrt(n) where n is the number of differences.

CB

Re: Paired difference T-Test

when you take the differences

this just becomes a one sample test.

t is appropriate when the population of differences is normally distributed

and you don't have the population variance from the population of all differences

Re: Paired difference T-Test

and what is this usual way?

Re: Paired difference T-Test

Quote:

Originally Posted by

**thomasboateng** and what is this usual way?

What is the formula for computing the SD form a sample?

CB

Re: Paired difference T-Test

yes this is my question what is the forumula for standard deviation.