When a man observed a sobriety checkpoint conducted by a police​ department, he saw 691 drivers were screened and 5 were arrested for driving while intoxicated. Based on those​ results, we can estimate that P(W)=0.00724 ​, where W denotes the event of screening a driver and getting someone who is intoxicated. What does P(W) ​denote, and what is its​ value?