Nested attributes

In a typical conjoint exercise, each concept includes a level for every defined attribute. However, in some studies, certain attributes only make sense when shown with specific options. Nested attributes (also known as alternative-specific designs) let you define these conditional relationships so that some attributes only appear for particular product concepts or configurations.

For example, consider a conjoint study showing several options for traveling around New York City on vacation. Attributes and levels might look like this:

With nested attributes, we can specify that Pick-up frequency and Subway/bus price appear only for Subway/bus, while Rideshare price and Congestion fee appear only for Rideshare. This will result in a concept that looks like this:

We can organize the attributes into three groups:

Primary attribute: The attribute whose levels appear in every product concept, and on which conditional attributes depend.

In this example, Mode of transportation is the primary attribute.

Nested attributes: Attributes that are displayed only with certain levels of the primary attribute.

In this example, Pick-up frequency and Subway/bus price appear only for Subway/bus, while Rideshare price and Congestion fee appear only for Rideshare. These attributes are blank when they don’t apply to a given concept.

Common attributes: Attributes displayed with all levels of the primary attribute.

In this example, Travel time is common and appears with all transportation options.

Creating nested relationships is straightforward.

1. Input all your attributes and levels.
2. Navigate to the Design tab of the exercise.
3. Next to Nested attributes, click Manage.
4. In the modal, click + Nest.
5. In the card that appears, select a Primary attribute.
       • In our example, the primary attribute is Mode of transportation.
6. Next to each level, select the Nested attributes.
       • For Subway/bus, choose Pick-up frequency and Subway/bus price.
       • For Rideshare, choose Rideshare price and Congestion fee.
7. Create additional nests, if needed. In our example, if we included the attribute Congestion fee cost, we could specify that attribute only appears if Yes is shown for the attribute Congestion fee.

Be careful not to overspecify dependencies. Nested rules do not have a transitive property.

For example, assume there are three attributes — A, B, and C — where B depends on A, and C depends on B.

• You would specify A as the primary attribute with B nested on a level of A.
• You would specify B as the primary attribute with C nested on a level of B.

You should not add a rule that A determines C. Each rule should define only direct dependencies.

When an attribute doesn’t apply to a product concept, it’s shown as blank. If your nested attributes are similar—such as the Subway/bus price and Rideshare price in the example—you can use Merged attributes to combine them and display them as a single attribute in the concept. Merging attributes does not affect utility estimation or market simulations.