alpha命令算的α值为何与手算的不同-经管之家官网！

最近在看《爱上统计学》第198页时发现，用stata命令alpha算量表的Chronbach's α值与书上手动计算或SPSS算的不同，想请教一下是为什么？数据在最后。stata计算α值显示 0.4365,而手算是0.24，差距很大。谢谢
. alpha a-e,i
Test scale = mean(unstandardized items)
average
item-test item-rest interitem
Item |ObsSign correlation correlation covariance alpha
------------- +-----------------------------------------------------------------------------------------------
a | 10 + 0.4719 0.2935 .1592593 0.3766
b | 10 + 0.2797 0.0000 .2314815 0.5051
c | 10 - 0.7775 0.4088 .0462963 0.1961
d | 10 + 0.6198 0.3331 .1055556 0.3065
e | 10 - 0.5572 0.1733 .1518519 0.4296
-------------+------------------------------------------------------------------------------------------------
Test scale | .1388889 0.4365
---------------------------------------------------------------------------------------------------------------
附数据：
a b c d e
3 5 1 4 1
4 4 3 5 3
3 4 4 4 4
3 3 5 2 1
3 4 5 4 3
4 5 5 3 2
2 5 5 3 4
3 4 4 2 4
3 5 4 4 3
3 3 2 3 2