Date: Fri, 7 Sep 2007 15:03:20 -0700
Reply-To: King Douglas <king_d@swbell.net>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: King Douglas <king_d@swbell.net>
Subject: Re: converting scales
In-Reply-To: <820E5CA81E7A2544A9D7E0A25025E4810131846A@e2k0305.chestnut.net>
Content-Type: text/plain; charset=iso-8859-1
The problem with using a simple linear conversion is that, depending on the two scales, neither the scale end-points nor the standard scores (z-scores) will be maintained.
Although you don't say it, I'm assuming you are talking about averages across a number of ratings, so maintaining z-scores is important. A simple linear conversion as suggested would underestimate the mean score, leaving more employees vulnerable to review.
I suggest using this formula:
New score = (old score - old scale midpoint)*(new range/old range) + new scale midpoint.
For instance, the converted score on a 4-point scale for a value of 3 on a 6-point scale would be
(3-3.5)*(3/5)+2.5 = 2.2
As opposed to 3*4/6 = 2 using the simple, linear transformation suggested below.
Using the formula above and converting from 6- to 4- point scale
1=1
2=1.6
3=2.2
4=2.8
5=3.4
6=4
King Douglas
American Airline Customer Research
elissa Ives <mives@chestnut.org> wrote: So in the new scale a value of 3 is comparable to 4.5 in the old scale
and a score of 2.67 is comparable to a value of 4 in the old scale.
Melissa
-----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
Oliver, Richard
Sent: Friday, September 07, 2007 2:42 PM
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: Re: [SPSSX-L] converting scales
If all you need is a simple linear conversion:
compute newscale=oldscale*(4/6).
-----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
Dee
Sent: Friday, September 07, 2007 2:26 PM
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: converting scales
I am trying to convert scores from an old scale to a new scale. The old
scale is a 1 t 6. Where 1 is the minumum value. The new scale is 1 to
4.
Where 1 is the minumun value. This scale is to be used for the HR
evaluation of employees where 1 is poor and 4 is excellent.
When using the old scale someone who received a 4.5 had to review their
performance with a supervisor and 4.0 with the VP. I am trying to find
the equivalent scoring for the 1 to 4 scale.
Director Institutional Research
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