student's t-test - (Jul/17/2007 )
can anybody help me understand student's t-test?
p<.005 or p<.0005 , what does it mean?
thx in advance
The p value from the t-test tells you whether the means are significantly different or not.
A p< or equal to 0.05 means the difference is significant.
Hope that helps,
Ceri
As far as I konw p is "the probability (possibility? I don't know the proper vocab.) that the null hypothesis is true".
So basically it should be the possibility your hypothesis is wrong. So the lower the p the "righter"!
As Ceri says, it helps you to identify if your data are significant; in graphs significant data are usually marked with * if p <0.05 or ** if p.< 0.01.
Hope this'll help you!
P value <0.05 means that the probability that you will get the value of the measurement as large as you have observed between the two samples U have studied occurring in the population just by chance is less than 5%.
Meaning that, suppose you are collecting data of two samples to see if the measurement between two samples are different. Let's say U r measuring height of boys and girls of same age. And, at the end of the experiment you come with a set of measurements for the two variables. You find the mean of height of boys and that of girls and determine the p value. Let's say the p value is <0.01.
This will mean that from the population of that age, if U randomly measure height of boys and girls, the chances of observing the difference between them just by chance is 1 in 10. So, 9 of the differences U got are real while 1 might have happened just by chance. So, higher the value of P, more likely that the observed difference was just by chance and does not happen in real.
p<0.05 is a randomly assigned value and it is assumption that if the probability of something happening just by chance is 1 in 20 then it can be considered to be significantly different.
I'd suggest to read a book about statistics (simplified one for biologists). If you don't have enough time for that, then you can check this page:
http://en.wikipedia.org/wiki/P_value
p value is not associated only with t-test, but with any kind of hypothesis testing. Cheers. 
Wrong. See below on the wikipedia page I linked (under Frequent misunderstandings). The coin flipping example and the interpretation clarifies what it is.
Thx to Ceri, Panda, Bungalow Boy and Kupac for kindly make some time to reply to my question. It helps me a lot.
regards
Wrong. See below on the wikipedia page I linked (under Frequent misunderstandings). The coin flipping example and the interpretation clarifies what it is.
If you need an easy to understand introduction, download the trial version of Prism 5 here. It comes along with several manuals, including the statistics guide. It is easy to understand!
K.
K.
thx krumelmonster