Measuring Bias or Measuring the Task: Understanding the Brittle Nature of LLM Gender Biases
This research addresses the brittleness of LLM gender bias evaluations, posing a puzzle for the NLP community about the ecological validity of benchmarks, but it is incremental as it focuses on measurement sensitivity rather than new mitigation methods.
The study investigated how signaling the evaluative purpose of a task affects measured gender bias in LLMs, finding that prompts aligned with gender bias evaluation framing elicit distinct gender output distributions and that discrete-choice metrics amplify bias compared to probabilistic measures.
As LLMs are increasingly applied in socially impactful settings, concerns about gender bias have prompted growing efforts both to measure and mitigate such bias. These efforts often rely on evaluation tasks that differ from natural language distributions, as they typically involve carefully constructed task prompts that overtly or covertly signal the presence of gender bias-related content. In this paper, we examine how signaling the evaluative purpose of a task impacts measured gender bias in LLMs. Concretely, we test models under prompt conditions that (1) make the testing context salient, and (2) make gender-focused content salient. We then assess prompt sensitivity across four task formats with both token-probability and discrete-choice metrics. We find that prompts that more clearly align with (gender bias) evaluation framing elicit distinct gender output distributions compared to less evaluation-framed prompts. Discrete-choice metrics further tend to amplify bias relative to probabilistic measures. These findings do not only highlight the brittleness of LLM gender bias evaluations but open a new puzzle for the NLP benchmarking and development community: To what extent can well-controlled testing designs trigger LLM "testing mode" performance, and what does this mean for the ecological validity of future benchmarks.