Coding the Information for Parameter Estimation

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The information in the core three sections of the ACBC questionnaires can be coded as a sequence of choice tasks and may be estimated using maximum likelihood estimation under the MNL model.  By default, non-price attributes are coded as part-worth functions using effects coding (a type of dummy coding procedure).


BYO and Most Likelies


The choice of level for each attribute may be coded as a choice task, where respondents chose 1 of K levels (traded off with price if level prices are being used within the Summed price feature). Thus, if 10 total attributes (other than price) are included in the study, this section will contribute 10 tasks.


If level(s) are omitted from a respondent's design (using constructed lists), the appropriate coding depends on whether the attribute involved has rational preference order.  For omitted levels for attributes without rational preference order (such as brand, color, etc.), we append additional information to the design matrix in the form of binary tasks and an additional "threshold" parameter.  The threshold "level" is "compared" to each of the included levels (at their component prices, if applicable) and "rejected"; then compared to all excluded levels (at their component prices, if applicable) and "chosen."  For levels missing from a respondent's design for attributes that have rational order, we do not add any new information to the respondent's data.  Rather, we suggest you apply monotonicity constraints for that attribute across the sample.


Screener Section


Each respondent has marked T concepts as "possibility" or "not a possibility."  We treat these each as binary choices, where the respondent is assumed to compare the utility of the concept to the utility of a constant threshold prior to making a choice.  The constant threshold is included in the design matrix as an additional dummy coded column.


Choice Tasks Tournament


These are coded as per standard CBC practice.

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