[R] Composite index reliability questions - cronbach()

[Jim Lemon]

Hi Nick,
If you haven't just made a typo on your example in QUESTION 2, the "This
doesn't" line should read:

cronbach(jdc[,c("Q1","Q2","Q3")])

Without the quotes, R looks for three objects named Q1, Q2 and Q3 and
probably doesn't find them.

Jim


On Sat, Sep 5, 2015 at 7:27 AM, Nick Petschek <nick.petschek at gmail.com>
wrote:

> Hi All,
>
> I have two questions on using cronbach() from the psy() package.
>
> My simplified situation is the following: I have a survey of 10 questions
> (column names are "Q1", "Q2", etc.) that went out to 100+ people. I have
> the responses to the questions, plus additional variables (demographics,
> location, etc.) in a data frame (named "JDC"). I want to build composite
> indices from these 10 questions. I plan to use two steps to create the
> indices. First, grouping the questions by what makes intuitive sense given
> what they ask, and second, by testing the reliability of these groupings
> using cronbach().
>
> QUESTION 1
>
> Let's say I think Q1, Q3, and Q5 will make a good index. With my limited
> knowledge of R, I would think there's a way to say "run the reliability on
> these three variables in this dataframe". However, I have so far only been
> able to test the reliability of *adjacent *variables. For example, I could
> do:
>
> *cronbach(jdc[,1:3])*
>
> to test Q1, Q2, and Q3. Is there a way to test non-adjacent variables?
>
> I realize I could do something like:
>
> *trust <- jdc[, c("Q2", "Q7", "Q8")]*
> *cronbach(trust)*
>
> but that adds a few extra steps, and I have tons of questions and indices
> which would make that very cumbersome, especially since I will go through
> several iterations in testing potential indices.
>
>
> QUESTION 2
>
> Is there a way to refer to the column name when using cronbach(), instead
> of just the location of the variable? For example:
>
> This works:   *cronbach(jdc[,1:3])*
> This doesn't:* cronbach(jdc[Q1, Q2, Q3])*
>
>
> Thanks in advance for any insights, answers, words of encouragement, or
> alternate ways I could solve this puzzle.
>
> Nick
>
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>
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