Z-Test Vs T-Tests
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Jim Shelor.
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August 3, 2007 at 5:30 pm #47736
Dear Friends.
I have a question…i’ll be obliges in the forum can provide me with some answers to these…
When do we use 1 sample Z-test, especially when we say that a sample drawn may not follow a normal distribution and generally found to follow a t-distributions.
Also like there are 2 sample t-tests and paired t-tests how come there is no 2 sample Z-test or paired Z-test.0August 3, 2007 at 5:31 pm #159533
Quality is lifeParticipant@Quality-is-lifeInclude @Quality-is-life in your post and this person will
be notified via email.Hi,
z test is used when the sample size is more than 30 while t test is used for smaple size less than 30.0August 3, 2007 at 5:43 pm #159536Hi,
But in some situations even with samples more than 30 the data may be non-normal, in that case how can one use Z-test. I am sceptical of such thumb rules. One can not generalise all processe this way.
If all we work with are samples(which are supposed to follow t-distributions) and never populations then wy this Z-Test at all???
An what about 2 sample Z-test???
0August 3, 2007 at 6:20 pm #159540DD:The T-test was designed to handle sample sizes less than 30 (google Gosset). It is also very robust to deviations from normality. There are no circumstances where I would advise someone to use the Z-test over the T-test.Strictly speaking, the Z-test is a test for populations rather than samples. For example, if you look at the formulae you will see entries for sd(population) that are estimated by sd(hat).Cheers, BTDT
0August 3, 2007 at 7:46 pm #159548Wrong
0August 3, 2007 at 8:59 pm #159553
Jim ShelorParticipant@Jim-ShelorInclude @Jim-Shelor in your post and this person will
be notified via email.DD,
When using Variable Data, testing one sample mean against a standard:Variance known One mean Z-test
Variance unknown One mean T-test.
When using Variable Data, testing two sample means against each other:Variance known Two mean Z-test
Variance unknown:Variances assumed equal Two sample pooled T-test.
Variances assumed unequal Two sample T-test.
Paired Data Paired T-test
There is a two sample Z-test (see above).
There is no paired data Z-test because there is no need for one.
I hope this helps.
Regards,
Jim Shelor0 -
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