1. A method in a computing device for determining similarity between queries, the method comprising: storing frequencies of the queries during intervals, each frequency of a query for an interval representing a number of times the query was submitted by users to a search engine; for each of the queries, generating autoregressive integrated moving average (“ARIMA”) coefficients for that query based on the stored frequencies for that query; and for a pair of queries, calculating a similarity score for the queries based on a correlation between the ARIMA coefficients of the queries, the calculating including aggregating products, for each ARIMA coefficients, of a first factor of a first query of the pair and a second factor of a second query of the pair, a factor for an ARIMA coefficient of a query being a difference between the ARIMA coefficient and a mean of the ARIMA coefficients divided by a standard deviation of the ARIMA coefficients.