Broiler Hatching Eggs

I was told that the hatchability for the first 7 days may remain the same as of day one but would decrease @ 1% per day after that. I am of the opinion that it may drop by 1% per week of holding. Has some one done study on this and can you enlighten me. What i am looking for is an answer to say if I hold for 7 days what is the hatch % loss, for 14 days what is the loss and 21 days what is the loss etc.