Another example: I am into calisthenics but mostly all YouTube channels featuring this topic show rather small men (170 - 175cm) that show off the most cool exercises. Why? Because calisthenic requires a lot a lever work. The smaller the human, the easier the work, the more successfull the journey, the more likely one is to start a channel on YouTube.
Since the planes were all constructed equally they were able to draw conclusions about the received damage. PE is not executed like planes are build - highly standardized meeting a lot of quality control. To actually draw a sample thats reliable, objective and valid, you would end up introducing variables like "method", "time", "equipment" etc. "Method" alone is a variable that is very intricate since some of us just wing it and others choose a more scientific approach. I believe once conrtolled for that you could see that people following a scientific approach bring more motivation and more time spend on PE with them.