Research and advocacy institutes are often known as "think tanks". A think tank is an organization that conducts research and advocates in areas such as social policy. Think tank reports are another useful way to pursue research on policy issues.
Search across many think tanks/research institutes:
Here are a few selected national think tanks/research institutes that work in areas relevant to social welfare:
Want a good overview of current and past federal policies? See if there's a Congressional Research Service report! CRS is the public policy research arm of Congress. This legislative branch agency works exclusively for Members of Congress, their committees and their staffs.
The following are just a few examples of local organizations working in specific areas of public policy. The Oregon Policy Directory also has a list of many organizations: Oregon Policy Directory
If you are looking for research and advocacy organizations in other states or local areas, Google is your best bet. Just be sure to view the websites with a critical eye and determine how legitimate they are. For example, does the organization list their staff and their creditials? Do their reports have scholarly references or do they just cite themselves or popular media?