Ranking

Ranking is the process of ordering a set of items according to a defined criterion or set of criteria. Unlike simple ratings that assign a score to each item, a ranking places items in order from best to worst. Rankings may be ordinal, with no specified difference between adjacent positions, and may include ties.

A ranking system typically includes: the items to be ranked, the criteria or features used to evaluate them, a scoring function or weighting scheme, and a method to convert scores into a final order. Data quality, measurement validity, and the treatment of ties or missing values all influence the reliability of the result.

Common methods range from simple scoring and aggregation to more complex models. Pairwise comparisons, rank aggregation, and algorithms that derive a global order from interactions are widely used. Notable examples include PageRank for web relevance, Elo or Bradley-Terry models for competitive outcomes, and relevance scores in information retrieval and recommendations.

Rankings are used in search engines, online marketplaces, sports standings, academic or institutional rankings, and product assessments. They support decision making, benchmarking, and transparency but depend on chosen criteria and data. Rankings can influence behavior and may reflect biases or incentives to manipulate the results if not carefully designed.

Interpretation requires context such as the scope, time window, and coverage. Users should consider the criteria, weightings, and limitations before acting on rank positions. Related concepts include sorting, evaluation, and ranking algorithms.