• Is the data from a reputable source, with a track record of reliability?
• Is the methodology, analysis method or data collection method appropriate and aligned with field standards?  
• Is the sample size appropriate?  Are there missing values or inconsistencies?

Think tanks are research institutes or organizations that conduct research to advocate solutions to social problems.  They may be:

• Non-partisan  (NBER, Rand Corporation)
• Centrist  (Brookings Institute, PEW Research)
• Liberal  (Center for American Progress, Center on Budget and Policy Priorities)
• Conservative  (Cato Institute, Heritage Foundation)

Non-partisan is not synonymous with non-biased, however.  And bias is not necessarily a bad thing, but it is important to be aware of it.

Consider the following:

• Check for an "about us" page.  Who writes for this organization.  Look for further info about authors.
• What topics do they cover?
• Is the purpose to share info or influence?
• Is more than one side/perspective covered?
• How is the organization funded?

Further information:

• check out Georgetown University Library's page on using think tank research.