Many people start their work with AI by prompting the machine to imagine it is an expert at the task they want it to perform, a technique that boffins have found may be futile.

Persona-based prompting – which involves using directives such as "You're an expert machine learning programmer" in a model prompt – dates back to 2023, when researchers began to explore how role-playing instructions influenced AI models’ output.

It's now common to find online prompting guides that include passages like, "You are an expert full-stack developer tasked with building a complete, production-ready full-stack web application from scratch."

But academics who have researched this approach report it does not always produce superior results.

In a pre-print paper titled "Expert Personas Improve LLM Alignment but Damage Accuracy: Bootstrapping Intent-Based Persona Routing with PRISM," researchers affiliated with the University of Southern California (USC) find that persona-based prompting is task-dependent – which they say explains the mixed results.

For alignment-dependent tasks, like writing, role-playing, and safety, personas do improve model performance. For pretraining-dependent tasks like math and coding, using the technique produces worse results.