Nested attributes

In a typical conjoint exercise, each concept includes a level for every defined attribute. In some studies, certain attributes only make sense in the context of specific options. Nested attributes, also known as alternative-specific designs, let you define these conditional relationships so that some attributes only appear for particular levels of another attribute.

For example, consider a conjoint study on ways to get around New York City. Attributes and levels might include:

With nested attributes, Pick-up frequency and Subway/bus price appear only for Subway/bus, while Rideshare price and Congestion fee appear only for Rideshare.

Nested designs use three types of attributes:

• Primary attribute: Appears in every concept. Other attributes depend on its levels. In this example, Mode of transportation is the primary attribute.
• Nested attributes: Appear only with specific levels of the primary attribute. In this example, Pick-up frequency and Subway/bus price are nested under Subway/bus price, while Rideshare price and Congestion fee are nested unser Rideshare. These attributes are blank when they don’t apply to a concept.
• Common attributes: Appear with all levels of the primary attribute. In this example, Travel time is common to all transportation options.

Creating nested relationships is straightforward.

1. Input all attributes and levels.
2. Navigate to the Design tab of the exercise.
3. Click Manage next to Nested attributes.
4. In the modal, click + Nest.
5. Select a Primary attribute — In this example, Mode of transportation.
6. Next to each level, select the nested attributes.
       • For Subway/bus: Pick-up frequency and Subway/bus price.
       • For Rideshare: Rideshare price and Congestion fee.
7. Add additional nests, if needed. For example, if the exercise included a Congestion fee cost attribute, you could specify it only appears if Congestion fee is set to Yes.

Be careful not to overspecify dependencies. Nested rules do not have a transitive property — each rule should define only direct dependencies.

For example, if B depends on A and C depends on B:

• Specify A as the primary attribute with B nested on one of its levels.
• Specify B as the primary attribute with C nested on one of its levels.
• Do not add a rule linking A directly to C.

When a nested attribute doesn't apply to a concept, it appears blank. If nested attributes are similar — such as Subway/bus price and Rideshare price — you can use merged attributes to combine them into a single display row. Merging is purely visual and does not affect utility estimation or market simulations. See the Merged attributes article for more.