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If I got a t -value=1.46988E-27, what does it signifies? How to find whether it is significant or not? And in what level it should be compared eg. 0.05 or 0.01 etc.

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What do you mean by t-value? The p-value of the test, or the value of the t statistic? What do you mean by pre- and post- test significance (I am not aware of signficance before doing a test)? – gui11aume May 26 '12 at 15:40
-1, please provide more details. – mpiktas May 28 '12 at 17:31

closed as not a real question by whuber♦ May 28 '12 at 18:52

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Of course that p-value indicates extremely high significance. But data are not exactly normal and the test statistic should not be considered exactly t under the null hypothesis. So the exact p-value should not be taken too seriously. The SAS Institute with their SAS software does not quote p-values below 0.0001 and will just call such a p-value as less than 0.0001 which I think is much more appropriate than quoting the exact p-value.

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It appears as though the $t$-statistic is $10^{-27}$, which would almost certainly indicate non-significance. – Macro May 26 '12 at 16:47
@macro Yes you interpreted what the OP said literally which would indicate a t of almost 0 which would be non-significant. But I assumed he meant the tail probability for the t statistic because he is looking at it as an indication of significance and numbers that small are in practice often seen as p-value but rarely as calculated values for the test statistic. – Michael Chernick May 26 '12 at 17:02
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Normally it should be above 1.65 to be significant at alpha 0.5 (two tailed) yours is probably significant at an alpha level of 0.2 (if you have more than 6 participants). See a T table at: http://www.sjsu.edu/faculty/gerstman/StatPrimer/t-table.pdf All the best!!

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