SSI Web: What's New in 8.3

The bulk of the improvements are in the ACBC component. We also added a few features that improve the capabilities of CBC and MaxDiff.


ACBC Improvements

Alternative-Specific Designs

Until this software version, ACBC users have been limited to traditional experimental designs, where the attribute list is a common list applicable to all product alternatives. In v8.3, users can specify that certain attributes (with all their levels) are only applicable to certain levels (e.g. brands, styles, etc.) of a primary attribute. This will open up new possibilities for the application of ACBC. For example, if comparing desktops to laptop computers, the laptop has a battery whereas desktops do not. There may be a conditional attribute upon the presence of battery, such as three levels of battery life. With alternative-specific designs, the attribute Battery Life (with its three levels) would only occur with laptop computers.

Merged Rows

Especially with Alternative-Specific designs, it is possible that two or more attributes actually refer to the same topic. For example, two separate attributes involving processor speed could be associated with either desktops or laptops (the desktops tend to be faster). Rather than show these as two separate rows in the choice task display (e.g. with blanks when the desktop speed attribute doesn't apply to the laptop), you could merge these two attributes to be displayed on just one row with a generic attribute label in first column, making the display appear more clean and compact. For more information, please see Merged Rows.

Ability to Skip the Screener Section

Starting in v8.3, it is possible to skip the Screener section, meaning that the respondent can jump straight from the BYO question to the Choice Tournament, or right into the Choice Tournament (skipping both the BYO and Screener sections). Note: no "None" utility will be available if you skip the Screener section, unless you estimate the None utility using the optional Calibration section.

Improved Design Efficiency

V8.3 ACBC designs are significantly more efficient than before. Previous versions of ACBC have done a reasonably good job of achieving independence of the attributes (orthogonality), but v8.3 goes much further to increase the orthogonality of the experiments at the individual-level. Orthogonality is directly related to D-efficiency. V8.3 features a level relabeling/swapping routine that oversamples BYO levels at the same rate as before, but creates near-neighbor cards that have significantly higher within-respondent D-efficiency. Our tests suggest that v8.3 improves the D-efficiency (at the respondent level) by about 5%-40%, depending on the attribute list and questionnaire setup.

Test Design Routine

The previous ACBC software did not have a test design functionality, so it was not easy to test the adequacy of designs for individuals or to assess the damage from prohibitions prior to fielding a study, for example. V8.3 includes a test design routine that generates a few or hundreds of "robotic" respondents (where the respondents answer randomly) and provides key statistics regarding the quality of the designs: level frequency, balance, d-efficiency, and standard errors (precision) of the utility parameters. It reports how often each level was shown to each respondent, so it is easier to adjust the questionnaire settings to target the "show each level at least twice and preferably three times per respondent" rule.

Avoiding Dominated Concepts

A dominated concept is a product alternative that is logically inferior to another concept (based on the Preference Order settings the researcher specifies). Researchers have found that avoiding dominated concepts in conjoint designs adds only a very little to the quality of the final utility results. However, it avoids the situation which sometimes bothers clients and respondents, where an obvious question is asked that might make that person doubt the logic behind the questionnaire. V8.3 allows the researcher to specify whether to avoid dominated concepts. Some degree of level balance and orthogonality is typically lost when avoiding dominated concepts (since it is just another form of prohibition that hinders the experimental design). Depending on the study setup, it could be a relatively minor or a major effect upon the design quality. The new Test Design routine can help you assess the impact of avoiding dominated concepts on the precision of utility estimates.

Ability to Customize the "At Most" and "At Least" Text by Attribute

In the "Must Have" questions, for attributes with a researcher-specified order ( best to worst or worst to best ) we often ask respondents if they must have "At Least" or "At Most" some level of an attribute. In previous versions of the software, the same global text for these phrases needed to apply to all attribute levels. Some researchers requested the ability to customize the text by different attributes and v8.3 supports this.

Interaction Search Tool

For v8.3 a new aggregate logit utility estimation procedure is available to help researchers investigate which interaction effects are potentially most significant. This routine automatically estimates utilities for main effects only, then runs main effects plus each possible two-way interaction effect (examined one at a time). It summarizes the results by listing the interaction terms in order from most to least significant in terms of the p-value as computed from a 2-log likelihood test. In our experience, most ACBC researchers ignore interaction effects and use main effects only (since adaptive ACBC designs don't support a convenient Counting Analysis report for 2-way interaction effects like CBC does). Yet, ACBC designs are well suited for estimating interaction effects. This automated routine should take away excuses for not investigating potential interaction effects. The most significant interaction effects found by this automated tool under aggregate logit are probably good candidates for inclusion in the final HB modeling.

Option to Take BYO Concept Forward to Choice Tournament

With v8.3, the researcher can specify that the respondent's BYO-selected "ideal" product should be carried forward into the Choice Tournament. For situations involving Summed Price or when not all attributes are shown in the BYO question, this can make a lot of sense (and lead to a richer Choice Tournament). But, for cases in which all attributes are shown in the BYO question and summed pricing is not involved, the BYO concept should dominate any other concept that the experimental designer could generate, so it may not be advisable to carry the BYO concept forward to the choice tournament.

Ability to Exclude Certain Attributes from "Must Have/Unacceptable" Probes

Some researchers have asked us to make it possible to exclude certain attributes from the Must Have/Unacceptable probes. Prior to v8.3, Price was the only attribute that the researcher could exclude from these probes. With v8.3, the researcher has full flexibility, by attribute, regarding the probes. However, we caution the user that excluding an attribute from Must Have/Unacceptable probes may potentially affect the utilities in undesirable ways. For example, an attribute involving levels allowed to be marked as Must Have or Unacceptable can get larger extremes in utility than attributes excluded from these probes.

Covariates in ACBC/HB Utility Estimation

We've extended the same capabilities that CBC/HB has regarding the use of covariates into the HB routine for ACBC. Covariates are typically profiling or usage-based data on respondents. For example, respondent income could be used as a covariate in HB estimation. If income were applied as a covariate, then when respondents are "smoothed" toward the mean via Bayesian shrinkage, they are mainly smoothed toward the mean utilities of respondents who are like them on the value of the covariates. So, for example, low income respondents would mainly be influenced by other low income respondents with respect to the data borrowing mechanism.

More Flexible Utility Constraints

During utility estimation, the researcher can specify that certain levels must be preferred to other levels within an attribute. This can make a lot of sense if the attribute truly has a logical preference order that all respondents would agree upon. Previously, there were limitations in the way that utility constraints could be specified. For example, you could not specify that level 1 > level 2; and level 3 > level 4 (without also indicating how levels 1 and 2 related to levels 3 and 4). With v8.3, the new dialog lets the researcher specify multiple independent chains of ordinal constraints within an attribute.

Record and Export Tournament Concept Order

In previous versions of ACBC, if you examined the way the data were stored for the Choice Tournament, it would appear that the respondents always picked the first concept from each set. That's just due to a shortcut we took in programming where we rearranged the concept order that was actually shown to respondents and recorded the chosen concept always in the first position. This bothered some ACBC users, because they wanted to be able to examine the original order of the concepts as shown to respondents. So, starting in v8.3, we are now saving the concept order as was seen by respondents.

Not Applicable (Missing) Levels in Conditional Display

If you have an Alternative-Specific design in ACBC then it is possible for you to need to specify in a conditional display table what is displayed when a missing level occurs. The 0 level in the table represents the not applicable level.