TL;DR
Three-tier classification is a content-filtering method where the LLM sorts items not with a binary "yes/no" but into three categories with explicit criteria: relevant, partially relevant, irrelevant. Each category is described in the prompt through concrete signals. The output format is locked down: the model returns exactly one of three words.
The study found that small models (Llama 3 8B, Qwen2.5 7B) perform almost as accurately as GPT-5 and Gemini 2.5 Pro once you add 2-3 classification examples (few-shot). Without examples, the small models beat GPT-5 (both API versions) but lost to Gemini 2.5 Pro. With examples, they caught up with Gemini. With the right prompting, model size stopped being the deciding factor.
The models rely on valid semantic signals (a virus mentioned alongside cancer, cause-and-effect wording), but sometimes latch onto random textual artifacts: deleting individual words flipped the decision. The more detailed the criteria and the more examples, the more stable the classification.
Want this for your own case? Apply this study to your task: AI adapts its method to what you are working on and writes the prompt.
Method Blueprint
PROMPT:
├─ Classification question
├─ Criteria for category 1 (relevant): list of signals
├─ Criteria for category 2 (partial): list of signals
├─ Criteria for category 3 (irrelevant): catch-all category
├─ [Optional] 2-3 examples with explanations (few-shot)
└─ Output format: strict instruction to return one word
OUTPUT: One word from the three categories
Runs in a single request.
Example in Practice
Task: You're filtering 200 AI papers for a subscriber newsletter. You only want the ones with practical prompting techniques, not theory or infrastructure.
Prompt:
How useful is this paper for a reader who works with ChatGPT/Claude in a chat window and wants to learn new prompting techniques?
A **Relevant** paper:
- Describes a ready-to-use prompting technique that works in chat (Chain-of-Thought, Few-Shot, Role Prompting, etc.)
- Provides prompt templates or examples you can copy
A **Partially relevant** paper:
- Mentions prompting, but focuses on theory or benchmarks
- Explains how LLMs work in a way that aids understanding, but offers no ready-made techniques
An **Irrelevant** paper:
- Is about fine-tuning, model training, infrastructure, API development
- Is about applying LLMs without a focus on prompting
**FORMAT:** Answer with one word only: Relevant, Partial, Irrelevant
---
[Paste the paper's title + abstract]
Result:
The model returns a single word. You filter 200 papers in 2-3 minutes: copy the prompt, paste the text, get the category. Relevant ones go into the newsletter, partial ones get parked for later, irrelevant ones get skipped.
Why It Works
In "yes/no" mode, an LLM tends to flatten the gray zone: a paper might be partly useful, but the model shoves it into one extreme or the other. Three categories create room for nuance: if a paper mentions the topic but offers no practical value, it's "partial," not "no."
Detailed criteria act as a checklist inside the model's head. Without criteria it relies on a generic semantic match ("the words look similar, so it's relevant"). With criteria it checks specific signals: is there a cause-and-effect link? Are there practical examples? That beats "looks on-topic" by a mile.
Few-shot examples calibrate the category boundaries. The model sees: this paper mentions both terms but draws no link, so it's "partial." This one explains a mechanism, so it's "relevant." Without examples the model invents the boundaries itself; with examples it copies the pattern.
A strict output format ("one word only") cuts off explanations and hedging. The model can't write "probably relevant, but...": it has to choose. That speeds up processing and makes the result machine-parseable.
Control Levers
- Number of categories → drop to two (relevant/irrelevant) for simple tasks or expand to four or five for finer sorting
- Criteria detail → the more detailed, the more stable, but the longer the prompt; you can simplify to 1-2 signals per category
- Few-shot examples → 2-3 examples sharply improve accuracy; beyond 5 the gains fade while token costs keep climbing
- Output format → you can let the model explain its choice after the category if you need transparency (but it'll be slower and harder to parse)
Prompt Template
How well does {item} fit the criterion: {your criterion}?
**{Category 1}** {item}:
- {Signal 1}
- {Signal 2}
**{Category 2}** {item}:
- {Signal 1}
- {Signal 2}
**{Category 3}** {item}:
- {Signal 1} OR does not meet the criteria above
**FORMAT:** Answer with only one of three words: {Category 1}, {Category 2}, {Category 3}
---
[Paste the item's content: paper text, candidate profile, customer review, etc.]
What to fill in:
- {item}: what you're classifying: a paper, a résumé, a review, a comment
- {criterion}: what you're sorting by: usefulness for your audience, fit for a job opening, sentiment
- {Category 1/2/3}: category names: relevant/partial/irrelevant; good fit/maybe/no fit; positive/neutral/negative
- {Signal}: concrete indicators: topic mentioned, numbers present, cause-and-effect link, work experience, emotional tone
To boost accuracy (few-shot):
Add 2-3 examples after the criteria, before the format instruction:
**Example 1:**
[Item text]
→ {Category 1}
**Example 2:**
[Item text]
→ {Category 2}
**Example 3:**
[Item text]
→ {Category 3}
The examples should be edge cases, where the difference between categories isn't obvious. That's what tunes the model to nuance.
Limitations
⚠️ Random artifacts: The model can latch onto individual words instead of meaning. The study showed that removing a single term sometimes changed the category even though the meaning stayed the same. The more complex the criteria, the higher the risk. Fix: test manually on 5-10 items and check for stability.
⚠️ Subjective criteria: If the line between categories is fuzzy even to you ("creativity," "growth potential"), the model will give unstable results. Three categories won't save you if the criteria themselves are vague. Fix: operationalize your criteria: instead of "creativity," use "uses metaphors or unexpected comparisons."
⚠️ Context length: With long texts (>2000 words) the model may skim and miss details in the middle. Fix: for large documents, summarize first, then classify the summary.
Resources
Small Language Models Can Use Nuanced Reasoning For Health Science Research Classification: A Microbial-Oncogenesis Case Study
Authors: Muhammed Muaaz Dawood, Mohammad Zaid Moonsamy, Kaela Kokkas, Hairong Wang, Robert F. Breiman, Richard Klein, Emmanuel K. Sekyi, Bruce A. Bassett
University of the Witwatersrand (South Africa), OncoVectra (UK)