Always, always, always check the source. Manipulating numbers is easy, and people who are smart about it will avoid outright lying. A biased source hasn't necessarily fudged the numbers, but unless you can get a detailed rundown of their methodology from a third party, they shouldn't be trusted on their own. See if independent studies back them up, and then consider if those studies have a bias as well. When people on opposite sides of an issue agree on the numbers, there's a good chance those numbers are solid. Third party sources that don't have a dog in that particular fight are also great for confirming things.
This is why when people ask if RT is a reliable source, I say it's not trustworthy about shit that interests Russia, but for anything that doesn't interest Russia it's probably a better source for honest reporting than most western media. Western media is completely partisan while RT is only partisan within a much more narrow area.