# Grounding and Hallucination Control — AI Safety, Evaluation and Cost Control

Source: https://www.geekswithgeeks.com/en/ai-safety/io-grounding

> Tie answers to retrieved evidence and flag claims that the sources do not support.

## Answer from evidence

The best defence against hallucination is **grounding**: give the model the relevant source text (retrieval), instruct it to answer **only** from that text and to say when the answer is not there, and ask it to **cite** the passage. Then add a check that compares the answer with the sources. Even a crude check, such as how many of the answer's words appear in the source, can flag sentences that introduce new claims. Stronger checks use a second model or entailment classifier, with their own error rates.

## A crude support score, run

I ran this. The first sentence is fully covered by the source (1.0); the second adds "water damage and theft" that the source never mentions, so only half its words are supported (0.5). This is a teaching toy, not a production check.

```python
import re
src = "The warranty lasts 12 months and covers manufacturing defects only."

def support(sentence, source):
    w = set(re.findall(r"[a-z0-9]+", sentence.lower()))
    s = set(re.findall(r"[a-z0-9]+", source.lower()))
    return round(len(w & s) / len(w), 2)

for sent in ("The warranty lasts 12 months.",
             "The warranty also covers water damage and theft."):
    print(support(sent, src), sent)
```

Output:

```
1.0 The warranty lasts 12 months.
0.5 The warranty also covers water damage and theft.
```

## Allow "I don't know"

Models tend to answer even when they should not. Say explicitly in the instructions that a refusal to guess is correct, and test with questions whose answers are not in the documents.

**Quiz:** What is a good instruction for reducing hallucination in a document Q&A bot?

- [ ] Guess when unsure
- [ ] Always sound confident
- [ ] Never mention sources
- [x] Answer only from the provided text and say if it is not there

*Answer:* Answer only from the provided text and say if it is not there. Restricting the answer to supplied evidence and allowing "not found" removes the pressure to invent.