Date: Mon, 23 Mar 2009 12:45:26 +0000
Reply-To: Ruben van den Berg <firstname.lastname@example.org>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Ruben van den Berg <email@example.com>
Subject: Confidence interval for 2 (related) percentages based on a single
11 point Likert scale
I've the following situation:
A 11-point Likert scale (from 0 (very dissatisfied) through 10 (very satisfied)) has been used in order to assess overall satisfaction. Now, the answers are recoded as follows:
RECODE NPS (0 thru 6=1) (7 thru 8=2) (9 thru 10=3) into SAT_GR.
Now the percentage (SAT_GR=1) is subtracted from the percentage (SAT_GR=3) (category 2 is not used here). The result of this is INDEX (with a theoretical range from -100% to +100%).
Can a confidence interval be computed for INDEX and if so, how?
I know there's a paired samples (difference between 2 proportions) test but these proportions are based on two different items (e.g. "do you have a cat (y/n)" versus "do you have a dog (y/n)"). I guess these formulas won't hold for proportions based on a single item...
Any help is highly appreciated!
TIA and kind regards,
Ruben v.d. Berg
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