R
{{category R}}
!!!cronbach.alpha()
{{outline}}
----
 library(ltm)

!!データフォーマット 1が正解、0が誤答
{{pre
str(goi2007.dat)

'data.frame':	222 obs. of  40 variables:
 $ X1 : int  1 1 1 1 1 1 1 1 1 0 ...
 $ X2 : int  1 1 1 1 1 1 1 1 1 1 ...
 $ X3 : int  1 1 1 1 1 1 1 1 1 1 ...
 $ X4 : int  0 1 0 1 0 1 1 0 1 0 ...
 $ X5 : int  0 1 0 1 0 1 1 0 1 1 ...
 $ X6 : int  1 1 1 1 0 1 1 0 1 1 ...
}}

{{pre
> head(goi2007.dat)
  X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X12 X13 X14 X15 X16 X17 X18 X19 X20 X21 X22 X23 X24 X25 X26 X27 X28 X29 X30 X31
1  1  1  1  0  0  1  1  1  1   1   1   1   1   1   0   1   1   0   1   1   1   0   1   0   0   0   1   1   1   0   1
2  1  1  1  1  1  1  1  1  1   1   1   1   1   1   1   1   1   0   1   1   1   1   0   1   1   1   1   1   1   0   1
3  1  1  1  0  0  1  0  1  1   0   0   1   1   1   1   1   1   0   1   1   1   0   0   1   1   1   0   1   1   0   1
4  1  1  1  1  1  1  1  1  1   0   0   1   1   1   1   1   1   0   1   0   0   0   1   1   0   1   0   1   1   0   1
5  1  1  1  0  0  0  1  1  1   1   1   1   1   1   1   1   1   1   1   0   0   0   0   1   1   1   0   1   1   0   1
6  1  1  1  1  1  1  1  1  1   1   1   1   1   1   1   1   1   0   1   1   1   1   1   1   1   1   1   1   1   0   1
}}


!!実行
{{pre
> cronbach.alpha(goi2007.dat)

Cronbach's alpha for the 'goi2007.dat' data-set

Items: 40
Sample units: 222
alpha: 0.844
}}

!!係数だけを得る場合、オブジェクトに保存して、alphaを指定する

{{pre
> result <- cronbach.alpha(goi2007.dat)
> result$alpha
}}