Why Do They Sell Vanilla and Chocolate Ice Cream?

Total Unduplicated Reach and Frequency (TURF) analysis is a statistical technique used by researchers to determine the smallest set of product or service characteristics that satisfy the largest audience.

Suppose you are asking:

1. In which media outlets should we advertise our restaurant to reach the greatest number of people and stay within our advertising budget?
2. Which flavors of ice cream should we offer if we only have space for two?
3. What would be the incremental value of adding a third flavor?
   

By analyzing both the frequency and overlap of respondent preference from a set of available options, TURF analysis can help answer these questions.

Consider this simple example:

Q: Which of the following flavors of ice cream would you buy?

1. Vanilla
2. Chocolate
3. Strawberry
   

Then suppose we asked ten people this question and got the following replies:

Respondent	Vanilla	Chocolate	Strawberry
1		X
2	X		X
3	X
4	X
5		X
6	X		X
7			X
8	X	X	X
9		X
10	X		X

In this example, vanilla is the most common answer with six responses, strawberry is next with five, and finally chocolate with four. Based on this simple frequency analysis, if you were limited to only offering two of these flavors, you would chose vanilla and strawberry since those two flavors received the greatest number of mentions in your poll.

However, upon examining the responses further you see that there is a large overlap between people who would buy vanilla and people who would buy strawberry. In fact, four of the five people who would buy strawberry would also buy vanilla if strawberry weren’t an option. There is very little overlap between vanilla and chocolate. Only one of the four people who would buy chocolate also say they would buy vanilla.

TURF analysis examines all of the possible combinations of flavors and calculates how many people would buy at least one flavor from each set. Here are the full results:

People who would buy…	Frequency
Vanilla	6
Strawberry	5
Chocolate	4
Vanilla or chocolate	9
Chocolate or strawberry	8
Vanilla or strawberry	7
Vanilla or chocolate or strawberry	10

The first observation that can be made is that any combination of two flavors will satisfy more people than offering any single flavor. A second, more interesting observation is that the combination of vanilla and chocolate will satisfy more people than any other two-flavor combination even though individually, chocolate was not one of the two most preferred flavors.

The reason for this is that if you are already offering vanilla, the incremental value of also offering strawberry is low. In fact, only one person in the poll who would buy strawberry says he would not buy vanilla.

Ideally we would offer all three flavors of ice cream; however we stated in our initial question that we only have space for two. Suppose that we have only two dispensers, but have ample space in our freezer to store strawberry ice cream in the event that either chocolate or vanilla runs out. This data shows that it would be more detrimental if chocolate ran out than vanilla since the combination of chocolate and strawberry reaches more customers than the combination of vanilla and strawberry.

None of these new findings could be known by looking at frequencies alone. Understanding TURF analysis helps uncover new and interesting things in our data and makes it clear why they sell both vanilla and chocolate ice cream.

Will You Engage Me?

The emergence of online research has created an illusion that researchers now have an endless pool of survey respondents. But the competition for a share of a person's online time is fierce. There are far more enjoyable things to do online than answer long, monotonous, and poorly worded surveys.

According to Simon Chadwick, CEO of online sample provider Peanut Labs, the average response rate for email-based survey invitations has dropped from 20% five years ago to only 4% today. Attrition rates on many panels are now reaching 50% per year. If we as researchers do not engage respondents by offering an enjoyable survey-taking experience, we run the risk of this pool drying up.

Last week, Survey Sampling International (SSI) announced its Respondent Preservation Initiative; an industry wide call to action to preserve and protect the most valuable resource to researchers - the respondent.

"The Initiative is a full-scale program to educate, support, and direct the industry. It places the people who give their time and opinions to marketing research front and center because it is people who, by sharing their insights, help businesses stay informed and reduce risk in decision-making."

Many online sample providers are now beginning to measure their panel members' experience with particular surveys and are offering discounts to clients whose surveys are engaging and enjoyable. This, of course, is a euphemism for saying that they will charge you more if your survey is confusing, boring, or uninteresting.

Advantage Research supports SSI in the Respondent Preservation Initiative and encourages the rest of the research community to do so as well.

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