I wonder whether Kaggle contest organizers sometimes remove the data sets after the end of the contest, or is that made impossible by Kaggle's policies?
In my understanding the data of Kaggle contests remain available indefinitely each with their own rules for sharing and publication. However, I only know of one instance where the data was removed. Criteo Display Advertising Challenge data was removed from Kaggle's website but it's still available on Criteo's and it was also re-released with a more permissive license better suited for research and publication.
The rules are different for different problems.
Having been active for some time now, this is what I've observed (Note: I play with completed competitions too for practise, and I personally haven't seen any data set getting removed till now):
- Generally, the data for the recruiting problems and limited access problems are removed and/or encrypted, and one needs to answer a survey (for their recruitment DB's) for unlocking it.
- Rest all data which is openly provided by either NGO's or other companies are not removed.
The companies have an option for that. You can either opt for letting the data be there even after the contest or not.
But, as the data is created especially for the purpose of competition, companies aren't really skeptical about they being available in the open.