---
type: source
title: "When combinations of humans and AI are useful: A systematic review and meta-analysis"
author: "Michelle Vaccaro, Abdullah Almaatouq, Thomas Malone (@NatureHumBehav)"
url: https://www.nature.com/articles/s41562-024-02024-1
date: 2024-12-01
domain: ai-alignment
secondary_domains: [collective-intelligence]
format: paper
status: null-result
priority: high
triage_tag: claim
tags: [human-ai-teams, meta-analysis, decision-making, content-creation, oversight, performance]
processed_by: theseus
processed_date: 2026-03-18
extraction_model: "anthropic/claude-sonnet-4.5"
extraction_notes: "LLM returned 2 claims, 2 rejected by validator"
---

## Content

Systematic review and meta-analysis of 106 experimental studies reporting 370 effect sizes. Published in Nature Human Behaviour, December 2024. Searched interdisciplinary databases for studies published between January 2020 and June 2023.

**Main finding:** On average, human-AI combinations performed significantly worse than the best of humans or AI alone (Hedges' g = -0.23; 95% CI: -0.39 to -0.07).

**Task-type moderation:**
- Performance LOSSES in tasks involving decision-making (deepfake classification, demand forecasting, medical diagnosis)
- Performance GAINS in tasks involving content creation (summarizing social media, chatbot responses, generating new content)

**Relative performance moderation:**
- When humans outperformed AI alone → performance gains in combination
- When AI outperformed humans alone → performance losses in combination
- Human-AI teams performed better than humans alone but failed to surpass AI working independently

**Implication:** Human-AI teams do not achieve "synergy" — they underperform compared to the best individual performer in each category. The combination is worse than the better of the two components.

## Agent Notes
**Triage:** [CLAIM] — "human-AI teams perform worse than the best of humans or AI alone on average, with the deficit concentrated in decision-making tasks" — this is a specific, disagreeable, empirically grounded claim from the strongest possible evidence type (meta-analysis, 370 effect sizes)
**Why this matters:** Directly challenges the assumption underlying human-in-the-loop alignment: that combining human judgment with AI produces better outcomes. If human oversight DEGRADES decision quality when AI is better, the case for human-in-the-loop as an alignment mechanism weakens dramatically. This also complicates our KB claim about centaur team performance.
**What surprised me:** The DIRECTION-DEPENDENT finding. Humans help when they're better, hurt when AI is better. This is the automation overshoot mechanism — as AI improves, the case for human involvement weakens in domains where AI exceeds human capability, but economic/safety arguments still push for human oversight.
**KB connections:** [[centaur team performance depends on role complementarity not mere human-AI combination]], [[human-in-the-loop clinical AI degrades to worse-than-AI-alone]], [[economic forces push humans out of every cognitive loop where output quality is independently verifiable]]
**Extraction hints:** The task-type moderation is the key insight. Decision-making vs content creation distinction may map to verifiable vs subjective outputs.

## Curator Notes
PRIMARY CONNECTION: centaur team performance depends on role complementarity not mere human-AI combination
WHY ARCHIVED: This is the strongest empirical evidence (370 effect sizes, Nature HB) that human-AI combination is NOT automatically beneficial — it depends on relative capability and task type. Directly relevant to the automation overshoot question.


## Key Facts
- Meta-analysis covered 106 experimental studies published between January 2020 and June 2023
- 370 effect sizes were analyzed across the studies
- Overall effect size: Hedges' g = -0.23 (95% CI: -0.39 to -0.07)
- Published in Nature Human Behaviour, December 2024
- Task types showing losses: deepfake classification, demand forecasting, medical diagnosis
- Task types showing gains: summarizing social media, chatbot responses, generating new content
