Fixing Google's Aggregation of Search Volumes
Google Keyword Planner states that it groups the search volume of plurals, abbreviations, misspellings of words and the search volume of keywords where the ordering of words is different. It ignores stop-words. When you're analysing the search volume of a list of keywords, and have multiple versions of the same keyword in your list, this can lead to total search volumes being markedly overstated. This tool stems/lemmatizes keywords, sorts words within each query alphabetically whilst fixing misspellings, removing stop-words and shortening common abbreviations to create a 'canonical' version of each query. This can then be used to calculate a much truer search volume for your keyword list. More details on the process here.