Using CASE with a boolean value

Hi all,

I'm trying to use a case statement with a boolean value.  i.e.  if the value =
false then output 'NO', if value = true then output 'YES'.  This is what I
came up with

CASE booking.quiz
    WHEN booking.quiz=false THEN 'No'
    WHEN booking.quiz=true THEN 'Yes'
    ELSE 'No'
END

But, it isn't working.  Everything compiles and the rows returned are correct
but it still returns 'true' or 'false' rather than 'YES' or 'NO'.  I've also
tried this

CASE booking.quiz
    WHEN booking.quiz='f' THEN 'No'
    WHEN booking.quiz='t' THEN 'Yes'
    ELSE 'No'
END

and this

CASE booking.quiz
    WHEN booking.quiz='false' THEN 'No'
    WHEN booking.quiz='true' THEN 'Yes'
    ELSE 'No'
END

Anybody got any ideas?  Should the value be cast into a string?

Thanks

Tom Ansley