```Date: Mon, 23 Mar 2009 12:45:26 +0000 Reply-To: Ruben van den Berg Sender: "SPSSX(r) Discussion" From: Ruben van den Berg Subject: Confidence interval for 2 (related) percentages based on a single 11 point Likert scale Content-Type: multipart/alternative; Dear all, 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. EXE. FRE 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 _________________________________________________________________ What can you do with the new Windows Live? Find out http://www.microsoft.com/windows/windowslive/default.aspx [text/html] ```

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