Assuming the stats were using HMRC's definition of a Personal Services Company, that simply means that a lot of biologists have started or joined very very small companies. In fast, the only reliable definition of a "Personal Service Company" I could find was here: http://www.contractorcalculator.co.uk/what_is_a_personal_service_company.aspx
relating to contractors.
"And so the term personal service company began to be used by HMRC to describe businesses they considered as tax evaders and potentially the subject of tax investigations. "
And this is HMRC's take: http://www.hmrc.gov.uk/ir35/
Of course this is much more boring than assuming the statistics mean there are 165 prostitutes or escorts who could represent you in court.