Which sentence is correct? the observers up front were asked to set down so that the ones in the back could see. the observers up front were asked to sit down so that the ones in the back could see.

the answer is; comparing the frequency of collisions with and without the device

this makes the anti-collision system an independent variable and the collisions a dependent variable. if there are fewer collisions with an anti-collision system that without, then it can be stated that the system is a success. essentially, collisions under an anti-collision system are compared with the frequency of collisions by cars with the human drivers.