```Date: Thu, 29 May 2003 11:58:35 -0500 Reply-To: king.douglas@aa.com Sender: "SPSSX(r) Discussion" From: King Douglas Subject: Re: creating index scores ranging from 0 to 100 Comments: To: "Cohen, Lou" In-Reply-To: <6B8B84CF5F18D3118FAD0008C79142C604847D83@gobexchm2.bhsala.com> Content-Type: text/plain; charset="iso-8859-1" Lou: Questions of validity aside, I find the most reliable method to convert scores to a common index is to preserve the endpoints and midpoints and maintain the standard scores (z-scores) by applying the following formula. The following is probably overly annotated, but there it is. King Douglas American Airlines * The following formulae convert scores on a scale of one range into scores on a scale of another range, such that the z-scores are identical, and any score that represents an end-point or mid-point on the old scale also represents an end-point or mid-point on the new scale. * The basic formula is ((old score) - (old scale midpoint))*((new range)/(old range)) + new midpoint. or X = (Y-Mo)*(Rn/Ro) + Mn where X = Converted score Y = Original score Mo = Midpoint of original scale (e.g., 3 if scale is 1-5) Mn = Midpoint of new scale (e.g., 5.5 if scale is 1-10) Ro = Range of original scale (e.g., 4 if scale is 1-5 [5-1=4]) Rn = Range of new scale (e.g., 9 if scale is 1-10 [10-1=9]) EXAMPLE: To convert scores on a 1-5 scale into scores on a 1-10 scale: COMPUTE NEWVAR = (OLDVAR - 3)*(9/4) + 5.5. EXAMPLE: To convert scores on a 1-10 scale into scores on a 1-5 scale: COMPUTE NEWVAR = (OLDVAR - 5.5)*(4/9) + 3. * To check the accuracy of the conversions, run descriptives of old and new variables. * Include the subcommand /SAVE in order save the z-scores of both the original and the converted scores. * Any score that is an endpoint on the original scale should be an endpoint on the new scale. DESCRIPTIVES VARIABLES = OLDVAR NEWVAR /SAVE /SORT. * Next, run descriptives of the saved z-score variables to check the high and low z-scores, which should be the same for the original and the converted varibles. DESCRIPTIVES VARIABLES = ZOLDVAR ZNEWVAR /SORT. -----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU]On Behalf Of Cohen, Lou Sent: Thursday, May 29, 2003 11:28 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: creating index scores ranging from 0 to 100 I am having a bit of trouble creating an index score that ranges from 0 to 100 from a set of survey items. Would appreciate any helpful suggestions. The survey contains several scales. For instance, scale1 contains seven Likert items (strongly disagree=1 to strongly agree=5). From this set of seven items I wish to create a summated index score per record from these items. In another scale, there are 11 items. Once again I wish to create summated index score ranging from 0 to 100 from this set of 11 items. Please note there are missing values for some of items in the data base. Thanks in advance Lou Cohen Director, Strategic Planning & Research Baptist Health System 3500 Blue Lake Drive Birmingham, Alabama 35283-0605 Confidentiality Notice: The information contained in this email message is privileged and confidential information and intended only for the use of the individual or entity named in the address. If you are not the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this information is strictly prohibited. If you received this information in error, please notify the sender and delete this information from your computer and retain no copies of any of this information. ```

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