1. A computer-implemented method comprising: using one or more processors, processing a query to identify item listings that satisfy the query, each item listing comprising data representing one or more attributes of a product or service offered for sale; assigning a ranking score to each item listing that satisfies the query, the ranking score comprising a weighted sum of a predicted listing quality score and an observed listing quality score, the predicted listing quality score being determinable at a time of listing when no historical data is available to assess a performance of the item listing, and the observed listing quality score being derived from an assessment of a historical performance of the item listing based on historical data, a weight of the observed listing quality score increasing over time relative to a weight of the predicted listing quality score as a function of a time-based metric that increases as historical data for assessing the performance of the item listing becomes available; and presenting the item listings that satisfy the query in accordance with the ranking scores.