1. A computer-implemented method of assessing specificity of a search query, the method comprising: under the control of one or more computer systems configured with executable instructions, obtaining clickstream data associated with the search query, the clickstream data comprising: indications of items listed in search results presented to users in response to the users submitting the search query in a search engine; for each of the items, an indication of a number of times the item was listed in the search results and an indication of a number of first-clicks the item received, wherein a first-click occurs when a user clicks, previews, hovers, or otherwise interacts with an item first in time before the other items listed in the search results; for each of the items, determining a first-click probability value by dividing the number of times the users first-clicked the item by a total number of first-clicks received across all of the items listed in the search results; and determining a specificity score for the search query based at least in part on the first-click probability values of the items listed in the search results, wherein the specificity score for the search query indicates a uniformity of a distribution of first-clicks across the items presented in the search results, and wherein the distribution is indicative of how the first-clicks are spread across the items presented in the search results, wherein the more evenly distributed the distribution of first-clicks, the lower the specificity score and the more likely the search query is submitted by users with the intention of general searching, and wherein the more skewed the distribution of first-clicks, the higher the specificity score and the more likely the search query is submitted by users with the intention of specific searching.
3. The computer-implemented method of claim 1 , wherein the more evenly the first-click probability values are distributed across the items listed in the search results, the lower the specificity score and the more likely the search query is submitted by users with the intention of general searching.