# [R] reliability, scale scores in the psych package

William Revelle revelle at northwestern.edu
Tue Mar 10 17:03:42 CET 2009

```Ista,
As you figured out, psych reverses items by subtracting from the
maximimum + minimum possible for each item.  (i.e., for  items going
from 1 to 4, it reverses items by subtracting from 5).

If all of the items have the same potential range  then you can just
let it figure out the range by itself.  If they differ in their
ranges (some items are 0 - 1 items, some are 1-9 items, etc., then
you need to give it the maximum and minimum vectors to use.

The min and max are figured out from all the items used in an
inventory, rather than just the items used in a particular scale.
This makes particular sense when you are scoring multiple scales from
the same inventory.

In answer to your first question (what packages do I tend to use for
scale construction?), the answer is that I tend to use the psych
package for basic analysis, and then the sem package for structural
equation analysis.

Bill

At 10:45 AM -0400 3/10/09, Ista Zahn wrote:
><snip>
>>  Second question: I spent some time with the psych package trying to
>>  figure out how to use the score.items() function, and it's become
>>  clear to me that I don't understand what it's doing. I assumed that
>>  setting a key equal to -1 would result in the item being reverse
>>  scored, but I get weird results, as shown below. When I try to reverse
>>  score (by setting a value of -1 in the key), I get scale scores that
>>  don't add up (e.g., the mean score is reported as being larger than
>>  the maximum item score). How is the score.items() function intended to
>>  be used? Do I need to reverse score items before using score.items()?
>
>I did it again--it seems like I always figure out the answer just
>after I ask for help. The score.items() function needs to know the
>maximum of the scale in order to reverse score. For some reason, the
>maximum appears to be calculated from all the scores, not just scores
>that have a 1 or a -1 in the key. On a hunch I set the max argument to
>a vector of scale maxima, and it worked. I'm still interested in
>responses to question 1 though.
>
>Thanks again,
>Ista
>
><snip>

--
William Revelle		http://personality-project.org/revelle.html
Professor			http://personality-project.org/personality.html
Department of Psychology             http://www.wcas.northwestern.edu/psych/
Northwestern University	http://www.northwestern.edu/
Use R for psychology                       http://personality-project.org/r

```