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How to always show some brands, and show others some of the time (to reflect distribution)

I am conducting a simple CBC study, for brand preference.  The client has asked that we show some brands all of the time, and others some of the time, to reflect the existing distribution in stores.  I am interested in knowing the best way to do this.

I have done this by having one master attribute for brand, and then alternative specific attributes for the brands that are shown selectively.  Two I have used binary attributes for "on" / "off", and one I have used a 3 level attribute to reflect it being available a 1/3 of the time.  

Is this the best way to achieve this type of design, and are there any pitfalls I should watch out for? Currently the design appears to be well specified, with standard errors below 0.5 for main effects.

In addition, as a separate question, the client has asked that we do not vary prices within each task, but instead impose variation across tasks.  We will not be measuring price-preference, and could measure brand preference using simple counts.  In theory we could look at preference vs. none as all prices shift up and down in different tasks.  Has anyone done anything like this before?

Thank you in advance
asked Dec 5, 2014 by TJ Bronze (970 points)
retagged Dec 5, 2014 by Walter Williams

1 Answer

+1 vote
Best answer
Another trick you could consider is to do the following:

1.  Create a brand list where some of your brands are duplicated in the attribute list.  If you want a brand to be represented twice as often, list it twice in the attribute list.

2.  Ask CBC software to generate an experimental design.

3.  From the Design tab, click "Import/Export Design..." to export the design CBC built to a .CSV file that you can edit and modify in Excel.

4.  Use Excel to recode the brands back to a list where each brand is listed once.  For example, if you duplicated BrandX so that it corresponded to brand numbers 4 and 5, then recode all 4s and 5s to be just 4.  Save the modified .CSV file.

5.  Create a copy of your project using File + Save Study As.  Modify that copy to have a brand list in the CBC attributes dialog where each brand is just represented once (and matches the coding scheme you implemented in step 4).  Import the new design from the Design tab, "Import/Export Design..." button, overwriting CBC's old design.

Also note that if you want to implement other specialized design schemes such as your client is asking for, you can often do so via manipulations you make to the .CSV file containing the design CBC made.  Just make sure to test your design under Design Tab + Test Design... + Advanced Test  to make sure that the design you've customized still works well to estimate the utility effects you need to get for your study.
answered Dec 5, 2014 by Bryan Orme Platinum Sawtooth Software, Inc. (198,815 points)
selected Dec 5, 2014 by TJ
Thanks Bryan
It looks like you can't have non-unique levels for an attribute in the new Lighthouse Studio. Is there any workaround?