# What is Ranking evaluation metrics

##### Understanding Ranking Evaluation Metrics

One of the primary goals of any search engine is to deliver the most relevant results to the users. The relevance of a result depends on various factors such as the query intent, the quality of the content, and the level of user engagement. However, with an ever-increasing amount of data on the internet, it can be a challenge to filter out the right information for a specific search query. The solution lies in the implementation of ranking evaluation metrics.

Ranking evaluation metrics help search engines to determine the relevance and quality of the content and rank them accordingly. In this article, we will explore the different types of ranking evaluation metrics used in the search engine industry.

##### Types of Ranking Evaluation Metrics

There are various ranking evaluation metrics available in the search engine industry. Depending on the search engine requirements, the metrics can be used in different combinations. Here are some of the popular ranking evaluation metrics in use today:

###### Precision/Recall:

The Precision/Recall curve is a graphical representation of the tradeoff between precision and recall. Precision is the fraction of relevant documents that are retrieved, whereas recall is the fraction of relevant documents that are retrieved out of all the relevant documents in the database. The curve determines the optimal threshold for a search engine to return the best results.

Formula:
• Precision = Number of relevant documents retrieved / Total number of documents retrieved
• Recall = Number of relevant documents retrieved / Total number of relevant documents
###### Mean Average Precision (MAP):

MAP is a widely used ranking evaluation metric and is the average of the precision at various levels of recall. The metric calculates the average precision as a function of the recall of the documents. MAP allows search engines to evaluate how well their ranking algorithms are performing against specific queries.

Formula:
• MAP = (1/|Q|) ∑Q(AP(q))
• Where, |Q| is the number of queries in the dataset, AP(q) is the average precision of the query q
###### Normalized Discounted Cumulative Gain (NDCG):

NDCG is a ranking evaluation metric that determines the quality of search results based on the user's intent. It measures the effectiveness of a ranking algorithm by evaluating the ranking of a set of documents for a specific query. It pays more attention to the documents ranked higher, which is a better reflection of the user's preference for higher-ranked documents.

Formula:
• NDCG = (DCG / Ideal DCG)
• Where, DCG = ∑i=1n (2^{rel_i} - 1 / log2(i+1)) and Ideal DCG is the maximum DCG value that could be achieved for a query
###### Mean Reciprocal Rank (MRR):

MRR evaluates the effectiveness of a ranking algorithm based on the rank of the first relevant document. It calculates the average of the reciprocal rank of the correct answer, indicating how well the ranking algorithm is performing for all the queries.

Formula:
• MRR = 1/|Q| ∑Q(rank(q))
• Where, |Q| is the number of queries in the dataset and rank(q) is the reciprocal rank of the correct answer for the query q
##### Choosing the Right Ranking Evaluation Metrics

Choosing the right ranking evaluation metrics depends on the goals of the search engine and the user's intent. Different ranking evaluation metrics have their strengths and weaknesses, and combining them can result in more effective results. It is essential to have a thorough understanding of the requirements and the data sets before choosing the right metrics for a search engine.

##### The Importance of Ranking Evaluation Metrics

The search engine industry is continually evolving, with new algorithms being developed and new ranking evaluation metrics being introduced. The importance of ranking evaluation metrics lies in their ability to measure the effectiveness of these algorithms. By analyzing the performance of the algorithms, updates or new algorithms can be introduced to improve the relevance and accuracy of the search results.

##### Conclusion

Ranking evaluation metrics play a crucial role in the search engine industry. The metrics provide a way to determine how well the ranking algorithms are performing and which areas need improvement. Various ranking evaluation metrics are available, and the choice of metric depends on the goals of the search engine and the user's intent. By using the appropriate ranking evaluation metrics, search engines can continue to deliver more accurate and relevant results to the users.