t 检验中，计算出t值后如何直接算出P值？（不查t界值表）
如两独立样本均数 X±S X1±S1 通过方差齐性检验及正态性检验，根据公式算出了t及v（自由度）值。如何进一步根据t值及自由度v直接计算P值？（不查t界值表）
给出公式，我出80分！
请各位数学家们指点！谢谢
也可发邮件给我 [email protected]
可能我还没说清楚，数学功底比较差:(
就如这个网页
http://www.graphpad.com/quickcalcs/ttest1.cfm?Format=SD
当我输入两组数据后，点"Calculate Now"，返回如下的页面
Unpaired t test results
P value and statistical significance:
The two-tailed P value equals 0.3833
By conventional criteria, this difference is considered to be not statistically significant.
Confidence interval:
The mean of Group One minus Group Two equals -1.8300
95% confidence interval of this difference: From -6.0088 to 2.3488
Intermediate values used in calculations:
t = 0.8796
df = 50
standard error of difference = 2.081
我输入的两组数据是
Group Group One Group Two
Mean 23.7800 25.6100
SD 8.2100 6.7700
SEM 1.6420 1.3029
N 25 27
The two-tailed P value equals 0.3833 是怎么计算出来的？