User manual SPSS CONJOINT 14.0

[. . . ] SPSS Conjoint 14. 0 TM For more information about SPSS® software products, please visit our Web site at http://www. spss. com or contact SPSS Inc. 233 South Wacker Drive, 11th Floor Chicago, IL 60606-6412 Tel: (312) 651-3000 Fax: (312) 651-3668 SPSS is a registered trademark and the other product names are the trademarks of SPSS Inc. No material describing such software may be produced or distributed without the written permission of the owners of the trademark and license rights in the software and the copyrights in the published materials. Use, duplication, or disclosure by the Government is subject to restrictions as set forth in subdivision (c) (1) (ii) of The Rights in Technical Data and Computer Software clause at 52. 227-7013. [. . . ] For example: CONJOINT PLAN='CPLAN. SAV' /DATA='RUGRANKS. SAV' If only a plan file or data file is specified, the CONJOINT command reads the specified file and uses the active dataset as the other. For example, if you specify a data file but omit a plan file (you cannot omit both), the active dataset is used as the plan, as shown in the following example: CONJOINT DATA='RUGRANKS. SAV' You can use the asterisk (*) in place of a filename to indicate the active dataset, as shown in the following example: CONJOINT PLAN='CPLAN. SAV' /DATA=* The active dataset is used as the preference data. Note that you cannot use the asterisk (*) for both the plan file and the data file. Specifying How Data Were Recorded You must specify the way in which preference data were recorded. Data can be recorded in one of three ways: sequentially, as rankings, or as preference scores. These three methods are indicated by the SEQUENCE, RANK, and SCORE subcommands. You must specify one, and only one, of these subcommands as part of a CONJOINT command. 17 Running a Conjoint Analysis SEQUENCE Subcommand The SEQUENCE subcommand indicates that data were recorded sequentially so that each data point in the data file is a profile number, starting with the most preferred profile and ending with the least preferred profile. This is how data are recorded if the subject is asked to order the profiles from the most to the least preferred. The researcher records which profile number was first, which profile number was second, and so on. CONJOINT PLAN=* /DATA='RUGRANKS. SAV' /SEQUENCE=PREF1 TO PREF22. The variable PREF1 contains the profile number for the most preferred profile out of 22 profiles in the orthogonal plan. The variable PREF22 contains the profile number for the least preferred profile in the plan. RANK Subcommand The RANK subcommand indicates that each data point is a ranking, starting with the ranking of profile 1, then the ranking of profile 2, and so on. This is how the data are recorded if the subject is asked to assign a rank to each profile, ranging from 1 to n, where n is the number of profiles. A lower rank implies greater preference. CONJOINT PLAN=* /DATA='RUGRANKS. SAV' /RANK=RANK1 TO RANK22. The variable RANK1 contains the ranking of profile 1, out of a total of 22 profiles in the orthogonal plan. The variable RANK22 contains the ranking of profile 22. SCORE Subcommand The SCORE subcommand indicates that each data point is a preference score assigned to the profiles, starting with the score of profile 1, then the score of profile 2, and so on. This type of data might be generated, for example, by asking subjects to assign a number from 1 to 100 to show how much they liked the profile. A higher score implies greater preference. CONJOINT PLAN=* /DATA='RUGRANKS. SAV' /SCORE=SCORE1 TO SCORE22. The variable SCORE1 contains the score for profile 1, and SCORE22 contains the score for profile 22. 18 Chapter 4 Optional Subcommands The CONJOINT command offers a number of optional subcommands that provide additional control and functionality beyond what is required. SUBJECT Subcommand The SUBJECT subcommand allows you to specify a variable from the data file to be used as an identifier for the subjects. If you do not specify a subject variable, the CONJOINT command assumes that all of the cases in the data file come from one subject. The following example specifies that the variable ID, from the file rugranks. sav, is to be used as a subject identifier. CONJOINT PLAN=* /DATA='RUGRANKS. SAV' /SCORE=SCORE1 TO SCORE22 /SUBJECT=ID. FACTORS Subcommand The FACTORS subcommand allows you to specify the model describing the expected relationship between factors and the rankings or scores. If you do not specify a model for a factor, CONJOINT assumes a discrete model. The DISCRETE model indicates that the factor levels are categorical and that no assumption is made about the relationship between the factor and the scores or ranks. The LINEAR model indicates an expected linear relationship between the factor and the scores or ranks. You can specify the expected direction of the linear relationship with the keywords MORE and LESS. MORE indicates that higher levels of a factor are expected to be preferred, while LESS indicates that lower levels of a factor are expected to be preferred. They are used simply to identify subjects whose estimates do not match the expected direction. IDEAL. [. . . ] The table also displays Kendall's tau for just the holdout profiles. Remember that the holdout profiles (4 in the present example) were rated by the subjects but not used by the Conjoint procedure for estimating utilities. Instead, the Conjoint procedure computes correlations between the observed and predicted rank orders for these profiles as a check on the validity of the utilities. 35 Using Conjoint Analysis to Model Carpet-Cleaner Preference In many conjoint analyses, the number of parameters is close to the number of profiles rated, which will artificially inflate the correlation between observed and estimated scores. In these cases, the correlations for the holdout profiles may give a better indication of the fit of the model. [. . . ]