what is the ttest?
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 Garter
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 Joined: Wed Aug 24, 2005 5:17 pm
what is the ttest?
Could someone please explain to me what the ttest is?
From http://www.physics.csbsju.edu/stats/ttest.html
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Jelanen
"Student" (real name: W. S. Gossett [18761937]) developed statistical methods to solve problems stemming from his employment in a brewery. Student's ttest deals with the problems associated with inference based on "small" samples: the calculated mean (Xavg) and standard deviation (sdev) may by chance deviate from the "real" mean and standard deviation (i.e., what you'd measure if you had many more data items: a "large" sample). For example, it it likely that the true mean size of maple leaves is "close" to the mean calculated from a sample of N randomly collected leaves. If N=5, 95% of the time the actual mean would be in the range: Xavg± 2.776 sdev/N1/2 ; if N=10: Xavg± 2.262 sdev/N1/2 ; if N=20: Xavg± 2.093 sdev/N1/2 ; if N=40; Xavg± 2.023 sdev/N1/2 ; and for "large" N: Xavg± 1.960 sdev/N1/2 . (These "smallsample" corrections are included in the descriptive statics report of the 95% confidence interval.)
Google is your friend.
Jelanen
'It is futile to pretend to the public that we understand how an amoeba evolved into a man, when we cannot tell our students how a human egg produces a skin cell or a brain cell!'
Dr Jérôme J. Lejeune
Dr Jérôme J. Lejeune
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