When seeking out the validity, credibility, and reliability of a source there can be a vast array of sources to compare when seeking this answer. For example, when validating a source we can research the author and his or her background pertaining to the data in question. Data within a claim can be meant to sway the reader one way or the other, with this in mind, I look at who and what there is to gain from this claim. I can use the gun ban debate stewing in Washington for a great example.
President Obama has been pushing for tougher regulations and bans on specific fire arms and related accessories based upon the elementary school shooting in Connecticut implying that this will contest the amount of damage and casualties occurred in mass shootings when statistically more people are killed by drunk drivers in society compared to mass shootings, but yet anyone over the age of 21 can purchase any amount of alcohol.
However, even statistics can be swayed depending on the pool of interested parties involved. Some methods I use to determine the reliability of data is to first seek the source from which the data is from. Typically I then seek out other sources in which I can compare that specific data against to validate the data is solid and not transparent. I then will analyze the different sources to be sure there is somewhat of a streamline when these sources are compared.