Context-based user behavior data is collected from a search mechanism. This data includes, for a given query, user feedback (implicit and explicit) on the query and context information on the query. This information can be used, for example, to evaluate a search mechanism or to check a relevance model. This context-based user behavior data may include user information. In one embodiment, explicit feedback is requested from the user except when the user requests a pause in explicit feedback requests, or only periodically, in order to reach a target value for requests for explicit feedback. The explicit feedback may include feedback concerning results not visited, and concerning non-standard results. Implicit feedback will include particular data items such as requeries by a user.