"Up to 50% of tickets are dismissed when challenged." There is probably a high number (half according to them) of tickets that get dismissed because of selecti

"Up to 50% of tickets are dismissed when challenged." There is probably a high number (half according to them) of tickets that get dismissed because of selection bias. Tickets [that have been] challenged are probably challenged because they have a good chance of being dismissed due to reasonable issue. Challenging more [random] tickets will probably cause this number to fall.