1. A method comprising: by one or more computing devices, selecting from a set of query-suggestion pairs a first query, wherein: each query-suggestion pair from the set of query-suggestion pairs comprises a query and a suggestion; and the first query is the query of at least one query-suggestion pair from the set of query-suggestion pairs; selecting from the set of query-suggestion pairs a subset of query-suggestion pairs, wherein: the subset of query-suggestion pairs comprises one or more distinct query-suggestion pairs from the set of query-suggestion pairs; and the first query is the query of each query-suggestion pair from the subset of query-suggestion pairs; computing a Log Likelihood Ratio (LLR) value for each query-suggestion pair from the subset of query-suggestion pairs; ranking the subset of query-suggestion pairs according to their respective LLR values; removing from the subset of query-suggestion pairs all query-suggestion pairs whose LLR values are below a predetermined LLR threshold; computing a Pointwise Mutual Information (PMI) value for each remaining query suggestion pair from the subset of query-suggestion pairs; removing from the subset of query-suggestion pairs all query-suggestion pairs whose PMI values are below a predetermine PMI threshold; and constructing a ranked set of suggestions for the first query, wherein the ranked set of suggestions comprises one or more suggestions of the remaining query-suggestion pairs from the subset of query-suggestion pairs.