Joint and Separate Evaluation

What it is

Hsee's 1998 article, Less is better: When low-value options are valued more highly than high-value options, reported that the same options can be ranked differently depending on whether people see them one at a time or together. When options are evaluated jointly, the one with more desirable attributes is judged better. When they are evaluated separately, people rely on contextual cues and reference points, and an option that offers less can be rated higher.

An earlier paper by Hsee, from 1996, proposed the evaluability hypothesis as an explanation for preference reversals between joint and separate evaluations of alternatives. The 2023 replication discusses its results as implications for that hypothesis.

The replication was a preregistered close replication and extension of three of the 1998 studies, run by a team of researchers and published in Collabra: Psychology. Across 403 participants it was mostly successful. The less-is-better pattern in separate evaluation held in most of the studies. The more-is-better pattern in joint evaluation was weaker in some of them. Some exploratory extensions produced surprising results, which the authors present as open questions.

In effect

The finding matters wherever options arrive in different formats and are looked at in sequence. A buyer comparing proposals one at a time is, in effect, judging them separately, and each one is measured against whatever the previous meeting set as the reference point. Placing the proposals on one page changes the task to joint evaluation.

The article on choosing a branding agency draws a practical reading from this: ask every shortlisted team to answer the same written brief and the same questions, and score each on a single sheet whose criteria were fixed before the first meeting. That reading is an application. The studies behind the concept were not studies of agencies or proposals.

The idea also connects to an earlier article on how products are judged on too little information, which covers the original studies.

What it does not say

It does not say that joint evaluation always produces better decisions. The replication found the joint pattern weaker in some studies, and the authors raise open questions about their exploratory extensions.

It does not say that separate evaluation is always a mistake. Some choices are made one option at a time, and the finding describes what people lean on when they are.

It does not say anything about proposals, agencies or professional services. Those uses are applications of the idea and not results of the studies.

The summary of the 2023 replication on this page rests on its published abstract, so it gives no detail beyond what the abstract reports.

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