I'm trying to look at the internal consistency of a questionnaire consisting of 9 binary items.

I mainly use SPSS, but am using R to determine McDonald's Omega coefficient using the omega() function in the "psych" package.

The main output I get from the omega function is:

Alpha: 0.71

G.6: 0.79

Omega Hierarchical: 0.58

Omega H asymptotic: 0.7

Omega Total 0.83

The value of alpha is markedly different to the alpha that SPSS gives me: 0.559

0.559 is also the value that the coefficient.alpha() function in the "ltm" package, so I'm inclined to believe that one more than 0.71

When reading the SPSS file in R, I get the following error message (although I read somewhere else that it was irrelevant to the statistical calculations):

In read.spss(datafilename, to.data.frame = TRUE, use.value.labels = false) :

Unrecognized record type 7, subtype 18 encountered in system file

Can anyone tell me why the omega function gives me a different value for alpha?

And should I trust the other omega outputs?

And is the error message relevant?

Many thanks for any help,

Ben