Nice follow up! Yes, NLST was actually a real randomized control trial for lung cancer screening, done before it was known whether or not it was helpful. The t

Nice follow up! Yes, NLST was actually a real randomized control trial for lung cancer screening, done before it was known whether or not it was helpful. The trial eventually stopped once they had enough outcome based evidence. The statistic you mentioned is not used in assessing the effectiveness of screening. It does closely relate to what is though to be the causal mechanism that leads to effectiveness.