Have no fears. There are no strings attached to the publishing of facts. If it worries you just reword the data slightly, but even that's not necessary.The whole point of this type of data is not just that it is in the public domain, but that it's been released by the collators specifically for the public domain. On top of that, all compilers of surveys and facts love to see their work quoted - that's the whole point of it.
It does not matter who develops the data, once it is released it is public information. Yes, it would be nice to go to source to ensure that all the data sets are available and to ensure accuracy of reporting, but that does not affect anything in regards to copyright: the information is still in the public domain.
Again, if concerned - although there's no reason to be - just ensure that you cite the source.
Three quarters of people surveyed believe that 75% of statistics are useless. Source: Syzygy.
[edited by: Syzygy at 4:44 am (utc) on June 24, 2008]