Best Practices for LLM Evaluation of RAG Applications

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Chatbots are popularly used for their strong chat and reasoning abilities (provided by LLMs), and the integration of Retrieval Augmented Generation (RAG) architecture is becoming a key method for improving these chatbots. It merges the strengths of a knowledge base, using a vector store, with advanced generative models like GPT-3.5 and GPT-4. This combination helps chatbots avoid giving incorrect information, keeps their answers current, and allows them to use specific knowledge from different fields. Accurately assessing the quality of a chatbot’s responses, however, remains a significant challenge. Since there are no industry standards for this, companies often rely on people to grade the responses, which takes a lot of time and is difficult to do on a large scale. Furthermore, in the context of the rapidly growing and evolving chatbots market, advancements in AI and ML-based language models have propelled the market’s value to $12 billion in 2023, as reported by Juniper Research, with projections of growth to $72 billion by 2028. Developing guidelines to evaluate LLMs, with a focus on RAG applications, is an essential step to ensure their overall effectiveness.

Understanding LLM Evaluation

It is not just about measuring accuracy; it’s about understanding how well a model comprehends and generates language. In the context of RAG applications, this evaluation becomes even more crucial. RAG, which combines a neural language model with a retrieval system, improves the ability of LLMs to provide more accurate, relevant, and context-rich responses.

Evaluating chat assistants, especially those powered by LLMs, is difficult because they have wide-ranging abilities, and current benchmarks don’t effectively measure what people prefer. To tackle this, Lianmin Zheng and his research group looked into using LLMs themselves as judges for more open-ended questions. They studied how effective LLMs are as judges, considering challenges like biases related to position, wordiness, and self-promotion, as well as their limited reasoning ability. To check how well LLM judges align with what people prefer, they introduced two benchmarks. The first, MT-bench, is a set of multi-turn questions. The second, Chatbot Arena, is a platform where people crowdsource evaluations of chatbots. Their findings show that strong LLM judges, like GPT-4, are quite good at matching both controlled and crowdsourced human preferences, with more than 80% agreement – similar to the agreement level among humans. This means using LLMs as judges is a practical and clear method for approximating human preferences, which are usually difficult and costly to measure. Furthermore, their research indicates that the combination of new benchmarks with traditional ones effectively evaluates various versions of LLaMA and Vicuna models, and to support this, they have made the MT-bench questions, 3,000 expert votes, and 30,000 conversational interactions based on human preferences publicly available.

LLMs and RAG applications

Image generated by the author with DALL·E 3 illustrating the theme of exploring and evaluating the world of LLMs and RAG applications.

The Significance of LangChain Evaluation

LangChain evaluation, an integral part of this process, involves assessing the model’s ability to chain together language constructs effectively. This evaluation ensures that the LLM can not only retrieve relevant information but also weave it into coherent, contextually appropriate responses.

LangChain provides different kinds of evaluators to check the application’s performance and accuracy with various data types. LangChain’s evaluators come with ready-to-use setups and an adaptable API for customization to meet specific needs. Here are some evaluator types LangChain offers:

  • String evaluators check the predicted text for a given input, often comparing it to a reference text.
  • Trajectory evaluators are used for evaluating the full path of agent actions.
  • Comparison evaluators are designed to compare predictions from two different runs on the same input.

These evaluators can be used in various scenarios and with different chain and language model implementations in LangChain.

Aligning LLMs with user needs

LLM alignment is a key aspect of evaluation. This involves aligning the model’s outputs with the intended use case and user needs. In RAG applications, this means ensuring that the model retrieves and generates information that is not only accurate but also aligns with the specific requirements of the application. Aligning LLMs with what humans expect is now a major focus for researchers. The survey done by Wang and his team provides an in-depth look at the technologies used for aligning LLMs. It covers different aspects, starting with data collection. It discusses the best ways to collect high-quality instructions for aligning LLMs, such as using NLP benchmarks, human annotations, and help from sophisticated LLMs. The survey also reviews the latest training methods for LLM alignment. This includes supervised fine-tuning and both online and offline training based on human preferences, along with training approaches that use parameters efficiently. Another crucial part of the survey is about evaluating these human-aligned LLMs. It looks at various methods to check how effectively these models are aligned, using a detailed approach to assess them. As a valuable resource for everyone interested in improving LLMs to better meet human-oriented tasks and expectations, the survey is available for the public.


Best Practices for LLM Evaluation of RAG Applications

  • Reduce Risk
  • Simplify Compliance
  • Gain Visibility
  • Version Comparison

Approaches to LLM Evaluation

When evaluating LLMs, several methods are employed to ensure they perform well and meet certain standards:

  • Automated metrics: This method uses tools like perplexity, BLEU score, and ROUGE. These tools measure how similar the output of an LLM is to a set of reference texts. The idea is to use statistical methods to measure how well the LLM replicates human-like text. This approach is fast and can process large amounts of data, but it doesn’t always capture the nuances of language.
  • Human evaluation: In this approach, people assess the quality of the LLM’s responses. They look at factors like how fluent, coherent, relevant, and complete the responses are. Human evaluation is essential because it considers the subtleties and complexities of language that automated metrics might miss. However, it can be time-consuming and subject to individual biases.
  • Hybrid approaches: These approaches mix automated metrics and human evaluation. The goal is to get a balanced view of an LLM’s performance. By combining the efficiency of automated tools and the nuanced understanding of human evaluators, hybrid approaches can provide a more thorough assessment of an LLM.
  • Context-aware evaluation: This method focuses on how well LLMs respond in line with the given context. It’s important for an LLM to not just generate grammatically correct or fluent language but also to produce responses that are relevant and appropriate to the specific situation or conversation it’s engaged in. Context-aware evaluation checks this aspect, ensuring the model’s outputs are not just correct but also fit the context.
  • Error analysis: Error analysis is about diving deep into the mistakes an LLM makes. By identifying and studying the types of errors, researchers and developers can get insights into what needs to be improved in the model. This analysis is crucial for ongoing model refinement and development, as it helps pinpoint specific areas where the LLM is falling short.

Each of these approaches has its strengths and weaknesses. Combining them can offer a comprehensive picture of an LLM’s abilities and areas for improvement, ensuring the development of more effective and reliable language models.

Implementing Best Practices

Best practices for evaluating these models in RAG applications are comprehensive and varied, aiming to cover all aspects of LLM performance:

  • Defining clear evaluation goals and criteria: It’s important to have specific goals and criteria for evaluation. These should match the intended use and the experience desired by the users. By setting these benchmarks, you can accurately assess the quality of LLM responses.
  • Choosing appropriate evaluation metrics: Select metrics that accurately reflect the LLM’s performance, including accuracy, fluency, coherence, relevance, and task completion. Using a mix of metrics helps understand different facets of the LLM’s functionality.
  • Using diverse and representative data: The data used for evaluation should be varied and reflect real-world scenarios. This diversity ensures that the results of the evaluation are applicable in actual use cases and provide meaningful insights.
  • Incorporating human evaluation: Human judgment is crucial for assessing subjective qualities of LLM responses, such as naturalness, creativity, and user satisfaction. Establishing clear guidelines for human evaluators enhances the consistency and reliability of these assessments.
  • Automating evaluation processes: Automating the evaluation can make the process more efficient, saving time and resources. This allows for more frequent and thorough evaluations.
  • Evaluating individual components: Analyzing the performance of specific components within the RAG system, like the retrieval and generation modules, helps pinpoint areas that need improvement.
  • Considering out-of-context responses: It’s critical to check if the LLM can avoid generating responses that don’t align with the given context, especially in applications where context is key to providing accurate and relevant responses.
  • Handling incomplete and incorrect responses: Developing methods to evaluate and address responses that are incomplete or incorrect is important, considering how they affect the overall task or user experience.
  • Evaluating conversational coherence: For dialogue-based applications, assess how well the LLM maintains the flow of conversation, stays on topic, and responds appropriately to user inputs.
  • Addressing bias and fairness: Assess the LLM for potential biases that could reinforce existing social inequalities. This involves examining the responses for biases and identifying potential sources of bias in the training data and model architecture.
  • Promoting explainability and interpretability: Understanding how an LLM arrives at its conclusions is important for trust, debugging, and improvement. Techniques to evaluate explainability and interpretability are therefore crucial.
  • Adapting to diverse domains and applications: The evaluation should be adaptable to different domains and applications, with criteria tailored to each specific context and requirement.
  • Continuously evaluating and improving: Evaluating LLMs should be an ongoing process, adapting as the model evolves and is exposed to new data and tasks. This continuous monitoring helps identify improvement areas over time.


Evaluating LLMs in RAG applications is not just a technical necessity; it is an imperative step toward building more reliable, equitable, and efficient AI systems. As we have seen, the evaluation process encompasses everything from setting clear goals and criteria to using diverse data sets and ensuring the model’s fairness and explainability. This comprehensive approach is crucial because it ensures that LLMs perform effectively in real-world scenarios, align with user expectations, and uphold ethical standards.

Given the complexity and importance of the evaluation task, we invite all developers and stakeholders in the field of AI and machine learning to prioritize the evaluation of their LLMs in RAG applications. It is not enough to develop advanced models; we must also rigorously test and refine them. This commitment to excellence and ethical responsibility will not only improve the performance and credibility of your AI solutions but also contribute to the advancement of the field as a whole.

Therefore, take action now. Review your evaluation strategies, incorporate a range of testing methods, and continuously seek to improve your models. By doing so, you will be at the forefront of creating AI technologies that are not only innovative but also trustworthy and beneficial to all.


Best Practices for LLM Evaluation of RAG Applications

  • Reduce Risk
  • Simplify Compliance
  • Gain Visibility
  • Version Comparison

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