Dr. William:

My self-petitioned I-485 NIW case was approved last month at TSC. I am currently a software engineer with a lot of database administration experience. If I accept a job of 'Database Administrator' with salary increase, do you think this new job is 'similar' to my current job?   

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Answer:

For USCIS to determines whether an occupation is same or similar to the one in the green card application, they will use the Dictionary of Occupational Titles or or Similar Publications. 

All these sources tend to be rather vague in defining jobs, especially so in the computer industry. The safe way is to change jobs whose title and description almost matches the green card job. For the salary, try to keep salary figures close to old salary.