Multiple Dichotomies

One possible coding scheme that can be used when more than one response is possible from a given question is to code responses using Multiple dichotomies. For example, as part of a larger market survey, suppose you asked a sample of consumers to name their three favorite soft drinks. The specific item on the questionnaire may look like this:

Write down your three favorite soft drinks:

1:________ 2:________ 3:________

Suppose in the above example we were only interested in Coke, Pepsi, and Sprite. One way to code the data in that case would be as follows:





Case 1




Case 2




Case 3




In other words, one variable was created for each soft drink, then a value of 1 was entered into the respective variable whenever the respective drink was mentioned by the respective respondent. Note that each variable represents a dichotomy; that is, only "1''s and "not 1"s are allowed (we could have entered 1's and 0's, but to save typing we can also simply leave the 0's as blanks or as missing values). When tabulating these variables, we would like to compute the number and percent of respondents (and responses) for each soft drink. In a sense, we "compact" the three variables Coke, Pepsi, and Sprite into a single variable (Soft Drink) consisting of multiple dichotomies.

For more information on Multiple dichotomies, see Multiple Responses/Dichotomies - Introductory Overview. See also, Association Rules.