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May 28, 2017 at 0:39 history edited Glen_b CC BY-SA 3.0
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May 27, 2017 at 10:35 comment added Glen_b @宓辰羲 No. The t-test is still correct, the z-test is approximate, but as the sample size increases, the t-test gets closer to a z-test. Ultimately in sufficiently large samples it doesn't matter which you do, but if you truly had normality there's no particular reason to use the z-test over the t-test no matter how big the sample size. With computers to do the calculation, there's no need to replace the t with an approximation.
May 27, 2017 at 10:32 history edited Glen_b CC BY-SA 3.0
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May 27, 2017 at 9:50 comment added mcxmcx Thanks very much for the response@Glen,@Michael. Both of your answers are very helpful for me! I made a mistake that in this case, I should use the paired t test rather than unpaired one. I have another question. For the large sample(>30 data) with normal distribution, is the z.test more appropriate than t.test?
May 27, 2017 at 8:52 history edited Glen_b CC BY-SA 3.0
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May 27, 2017 at 8:30 comment added Michael R. Chernick This is a good answer. I like that you emphasized that the signed rank test is the appropriate form of the Wilcoxon test to use with paired data. I think it would also be good to distinguish that the paired t test should be used rather than unpaired t test.
May 27, 2017 at 6:45 history edited Glen_b CC BY-SA 3.0
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May 27, 2017 at 6:20 history edited Glen_b CC BY-SA 3.0
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May 27, 2017 at 6:08 history edited Glen_b CC BY-SA 3.0
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May 27, 2017 at 5:47 history answered Glen_b CC BY-SA 3.0