Pages: How to set report parameter for a decision box?

Pages: How to set report parameter for a decision box?

I am setting up a page what is showing a report. To filter elements by default there is the option to set parameters like:

  1. params='Name=John&&Doe'
This will show all lines, where the field "Name" contains "John Doe".

But how to search for the value of a decision box? I have tried:
  1. params='Booked=Yes'
and
  1. params='Booked=true'
but this doesn't have any effect. I receive always all available lines.

Any idea? Thanks for helping.