First of all - you just confused OR with AND ("OR" means it meets any of the conditions, "AND" means it must meet
all of the conditions). Since a person can't be listed as "Dr" and "Dr(Mrs)" at the same time, setting the parameter to "Dr" yeilds no records. I've rearranged it so I could follow the logic easier and came up with this:
if {?By Salutation} = "ALL" then TRUE 'this selects everyone
else (if {?By Salutation} = "Dr" then
{GP27.SALUTATION} = "Dr" or {GP27.SALUTATION} = "Dr(Mrs)" 'this gets the Doctors - men and women
else {GP27.SALUTATION} = {?By Salutation} 'this catches everyone else
Second - Are these the only choices for a salutation?

Haven't you heard of political correctness? In your case, these few may be acceptable for 99% of the people you'll deal with, but there's always that exception. A doctor can be a man or a woman, married or single. And a nurse can be a man or a woman and not necessarily a member of a religious order. A female doctor or nurse should have the choice to tell her marital status or religious affiliation or conceal it if she prefers.