We put together some interesting stats from across a handful of our clients on misspellings on internal search. We used a broad definition of a misspelling. If a search phrase contained a word which is not on the site then we count it as a misspelling. Obviously this will also include words that are spelled (or spelt?) correctly but just aren’t on the site. For example if you search for “razor” on Tupperware.com it’s not on the site anywhere so we would count that as a misspelling even though razor is spelled correctly. So this yields an upper limit.
The average was 10% of queries contained a word that wasn’t in the index. This was higher than I was expecting and emphasises the importance of having a spell checker on your site search and of paying attention to your search terms that have poor results (which is a larger set than the terms which contain words that aren’t in the index). Interestingly the client with the lowest rate of misspellings is one that pays a lot of attention to our report that shows search terms with poor results and regularly updates their synonyms to try and improve these.
