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Each taster in the choice experiment got a set of potato chips like this. Can you guess which one is the ketchup-flavored chip?
I grew up in Canada, where ketchup potato chips were a staple at most children's birthday parties. As a huge fan of these ketchup chips, I was unsure whether my enjoyment of the wonderful flavor was simply nostalgia and whether other people unfamiliar with the flavor would show any love for ketchup chips. Similarly, I’ve noticed that dill pickle flavored chips and the ever-popular "all dressed" flavor are uncommon here in the US compared with Canada.
After our chocolate smackdown was such a success with the JMP group, Melinda Theilbar and I were looking for another opportunity to conduct a choice experiment. To make it fun, we wanted the experiment to contain a number of flavors new to the tasters. The fortuitous timing of Lay’s chips new “Do Us a Flavor” campaign and a visit from my parents in Canada presented the perfect opportunity: potato chip smackdown!
While we figured that tasting chips would be not as popular as tasting chocolate, we also did not have as many worries about limiting the number of tasters due to limited resources -- the chip bags contained plenty of chips. The ideal mix of flavors for the experiment would be a combination of mostly unfamiliar flavors, with a couple of more familiar flavors thrown in. Although the chocolate experiment had six different chocolates among two factors (with two origins and three cacao contents), this time we have just one factor with more levels. We ultimately ended up with 10 flavors:
New York Reuben
Southern Biscuits and Gravy
West Coast Truffle Fries
Southern Heat Barbecue
Sour Cream and Onion
How to get the response?
What we want is a general ranking of the desirability of each of the flavors. One way to do this is to get tasters to provide their own ranking of the flavors. However, with tasting so many different flavors (and the fact that we didn’t want to stuff people with potato chips), this type of forced ranking seemed like it would be a difficult task requiring lots of little bites.
Picking the favorite among a smaller group of choices is much less demanding to the tasters, but carries less information. There are 45 (10 choose 2) different pairwise comparisons for the 10 potato chips. While we don’t require all of these pairs to appear in the survey, if we give tasters five or six pairs of chips, it doesn’t sound like we’re getting much information.
Another option: Size 3
Instead of choice sets of size 2, we decided to use choice sets of size 3. Doesn’t sound like a big deal? Consider this: In picking a favorite, we actually get information comparison information for the favorite versus each of those that were not chosen.
That’s not all
In addition to reporting the favorite from each choice set, we also had the tasters report their least favorite flavor from each choice set. If we just asked for the favorite in each choice set, we don’t get any information about the two flavors not chosen in relation to each other. By asking for the favorite and least favorite, we gain that information.
OK, but can you still analyze it?
Analysis is going to require some extra work, but it’s certainly doable within JMP. Melinda will go through the analysis next time (sorry, you’ll still have to wait for the results – no hints yet!).
We can use the Custom Designer to create a design in much the same way that we did for the chocolate experiment. It was decided that each taster would get four choice sets, and four different surveys would be created.
1. Add a false VHTC and false HTC factor to set up random blocks corresponding to surveys and choice sets, along with a 10-level factor for flavor.
2. Remove the false VHTC and HTC effects from the model.
3. Set up the number of whole plots for the total number of surveys (4), subplots the total number of choice sets (16 = 4*4), and the run size as the number of choice sets times the number of chip flavors per choice set (48 = 16*3).
Melinda and I have completed this experiment, but I don't know the results yet. The choice sets of size 3 did seem to be a good choice in this case, as the tasters found it reasonably easy to make the ranking for each set they were presented with. I didn’t have a notion that there was a clear-cut winner as the results were being collected, but there’s one particular flavor that I suspect will not fare very well. Thanks for reading!