General business slowdown layoffs are always random. Each product line is given a reduction target. Each line head then splits this target amount among various functional teams. Each project head then decides to fire the least important person in the team whose severance will not majorly impact the working of the project. The past performance is meaningless here  
 At the higher levels, sometimes people who decide to scrap the entire project, will fire off the whole team and show their targets to the sr. Management. 
 This is what I have seen in three companies.

Consultant

Program Manager

Google has been terminating the employment of many people, adding fuel to the growing discontent among employees.  A software engineer, who is seeing many people leaving, has vented out her frustration on LinkedIn, saying Google is randomly firing people.

Google is randomly firing people?