Read the passage.

[1] Pediatricians who have children of their own take better care of their patients. [2] Being a parent or guardian is a powerful and profound experience. [3] It changes doctors and gives them greater insight. [4] Doctor Stevenson disagrees with my argument. [5] However, his judgment is untrustworthy, since he is not a parent.

What type of logical fallacy is sentence 5?

a false dilemma
begging the question
a professional opinion
an ad hominem attack