The TIOBE Programming Community index is an indicator of the popularity of programming languages. The index is updated once a month … It is important to note that the TIOBE index is not about the best programming language or the language in which most lines of code have been written.
The index can be used to check whether your programming skills are still up to date or to make a strategic decision about what programming language should be adopted when starting to build a new software system.
So how does TIOBE calculate this index? You might not believe this, but they count the number of search engine results for each programming language. Not the number of people querying, not the number of queries they’re making, not sentiment. It relies entirely on that useless number that search engines report. (Source: TIOBE Index Definition)
To give themselves a veneer of being data driven they don’t check just one search engine (google.com), they check several (bing.com, google.de, google.co.in and a few others). But 25 useless sources isn’t any better than 1 useless source.