As covered in Part 1 of this post, the Title II Social Security and SSI programs are very different. Particularly, you can apply for Social Security disability online, but you cannot apply for SSI online and most download the application and take it into your local Social Security Office, where it can be filed. Make sure that the employee who receives it gives you a receipt.
Also, what information is crucial to understand each claim is very important, in particular since many people confused their differences.
One area in which they are the same is in the requirements to prove the medical disability (see Medical Conditions). They both use the medical listings, the same limitations as to: standing, sitting, walking, lifting weight, bending, stooping, kneelling, pushing, pulling, crawling, and crouching.
The same is true in the mental health listing limitations: memory, concentration, ability to understand and follow simple instructions to deal with co-workers, supervisors, and the public in general, and to be on task mentally.