They cite three possible explanations:

1. Possible undesirable discrimination (no objective reason)

2. Self-employment might be a valid signal they would not “fit” in the organization

3. Entrepreneurs may lack skills that can only be gained in employment

It is good to note that this was done through online job boards, and only accounts for an invitation for an interview. They applied to 100 positions (2 CVs each) over two years, and had a 11% total positive response rate. They also note that 70% of the positions were advertised by recruiters.

While the sample size is low, online job boards have always had a low response rate. And, recruiters might feel they can't sell/profit-from a self-employed person as well as a traditional wage earner.

This study was done in the UK. I wonder if it'd be different in the US.

Also the sample size should be increased by a factor of 10.