Generating an Orthogonal Design

Generate Orthogonal Design generates a data file containing an orthogonal main-effects design that permits the statistical testing of several factors without testing every combination of factor levels. This design can be displayed with the Display Design procedure, and the data file can be used by other procedures, such as Conjoint.

Example. A low-fare airline startup is interested in determining the relative importance to potential customers of the various factors that comprise its product offering. Price is clearly a primary factor, but how important are other factors, such as seat size, number of layovers, and whether or not a beverage/snack service is included? A survey asking respondents to rank product profiles representing all possible factor combinations is unreasonable given the large number of profiles. The Generate Orthogonal Design procedure creates a reduced set of product profiles that is small enough to include in a survey but large enough to assess the relative importance of each factor.

To Generate an Orthogonal Design

This feature requires the Conjoint option.

  1. From the menus choose:

    Data > Orthogonal Design > Generate...

  2. Define at least one factor. Enter a name in the Factor Name text box. Factor names can be any valid variable name, except status_ or card_. You can also assign an optional factor label.
  3. Click Add to add the factor name and an optional label. To delete a factor, select it in the list and click Remove. To modify a factor name or label, select it in the list, modify the name or label, and click Change.
  4. Define values for each factor by selecting the factor and clicking Define Values.

Data File. Allows you to control the destination of the orthogonal design. You can save the design to a new dataset in the current session or to an external data file.

  • Create a new dataset. Creates a new dataset in the current session containing the factors and cases generated by the plan.
  • Create new data file. Creates an external data file containing the factors and cases generated by the plan. By default, this data file is named ortho.sav, and it is saved to the current directory. Click File to specify a different name and destination for the file.

Reset random number seed to. Resets the random number seed to the specified value. The seed can be any integer value from 0 through 2,000,000,000. Within a session, a different seed is used each time you generate a set of random numbers, producing different results. If you want to duplicate the same random numbers, you should set the seed value before you generate your first design and reset the seed to the same value each subsequent time you generate the design.

Optionally, you can:

  • Click Options to specify the minimum number of cases in the orthogonal design and to select holdout cases.