Date: Sat, 5 Mar 2011 22:51:27 -0600
Reply-To: "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Subject: Re: Question about calculation of % change
The range on a 1 - 4 scale is 3 not 2.5 and the range on a 0 - 3 scale is also 3, so a 1 unit change is 33% either way.
Dr. Paul R. Swank,
Professor and Director of Research
Children's Learning Institute
University of Texas Health Science Center-Houston
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Max Freund
Sent: Saturday, March 05, 2011 7:58 PM
Subject: Question about calculation of % change
This is an embarrassingly basic question and not really SPSS-related, but I've got myself confused about it so I'm hoping this brain trust can help straighten me out.
I have a variable measured on a 1-4 Likert scale at Time 1 and Time 2. I want to compute the percent change from T1 to T2. Would it be more accurate to transpose the scores to a 0-3 scale before calculating the % change?
For example, a change from T1=2.5 to T2=3.5 measured on a 1-4 scale would result in a 40% increase (1/2.5=.4). When transposed to a 1-3 scale, however, it results in a 67% increase (1/1.5=.67). So basically, I'm wondering if starting the scale at 1 is a false minimum.
The variable in question is an average of several items rating different aspects of organizational capacity and management practice, with 1 being little to no capacity in that area and 4 indicating robust capacity.
Strictly speaking I know it may not be conceptually meaningful to compute percent changes in Likert items anyway (this one is actually an aggregate of several items). However, this is for an evaluation of a project that had as one of its objectives an X% increase in participants' capacity scores.
Max Freund, M.I.I.M. * firstname.lastname@example.org<mailto:email@example.com> * (909) 632-1624
Partner, LF Leadership (www.lfleadership.com<http://www.lfleadership.com/>)
Doctoral Student in Organizational Behavior, Claremont Graduate University (www.cgu.edu/sbos<http://www.cgu.edu/SBOS/>)
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