[R] psych package - Cronbach`s Alpha - warning message

[Ista Zahn]

Many of the statistics reported don't make sense with only two
items--for example the alpha if an item is dropped makes no sense
because dropping an item leaves only one remaining.

Best,
Ista

On Fri, Feb 14, 2014 at 5:24 PM, Johannes Moser <joh.mo at web.de> wrote:
> Dear R-help,
>
> I try to estimate alpha for a factor that loads onto two items, using
> the psych-package (newest version).
> The data is from the boston housing data set.
>
> The problem I face can be reproduced by the following approximation of
> the correlation matrix:
>
> library("psych")
> tt <- cbind(c(1,0.58) , c(0.58,1))
> colnames(tt) = rownames(tt) = list("V1" , "V2")
> alpha(tt)
>
>
> R Version 3.0.2 (2013-09-25) 64 Bit  -  Platform: Windows 7
> Professional, 64 bit
> I have tried on two different Windows computers - same warning messages:
>
> In matrix(unlist(drop.item), ncol = 6, byrow = TRUE) : data length [10]
> is not a sub-multiple or multiple of the number of columns [6]
>
> What is the reason for the warning?
> Is it to be taken seriously?
> How can I avoid this warning?
>
> I would be very thankful for any ideas or advice!
> Thank you a lot in advance!!!
>
>
>
>
>
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