For large numbers, 80% is what you'd expect. There are some situations that would make the numbers worse. For example, is Marc's potential attendance really 1/3 of Joseph's? And is Joseph's really 30%, or might it be 25%? Things happen when you reach large numbers that simply make 80% more valid than all this analysis. I just came back from a wedding. 550 invited. 452 attended. For purposes of planning the hall and starting to talk to the caterer, the initial estimate of 440 was fine.

May I offer a line from my toast to the couple? "Remember, if your wife is happy, but you are not happy, you are still far happier than if your wife is unhappy, but you are happy."

For large numbers, 80% is what you'd expect. This may be a situation where a detailed analysis as you propose only adds errors to the calculations. 
For example, is Marc's potential attendance really 1/3 of Joseph's? And is Joseph's really 30%, or might it be 25%? Things happen when you reach large numbers that simply make 80% more valid than all this analysis. I just came back from a wedding. 550 invited. 452 attended. For purposes of planning the hall and starting to talk to the caterer, the initial estimate of 440 was fine.

May I offer a line from my toast to the couple? "Remember, if your wife is happy, but you are not happy, you are still far happier than if your wife is unhappy, but you are happy."

For large numbers, 80% is what you'd expect. I'm sorry if this is not a 'stats' answer, but there are some situations that the numbers make it worse. For example, is Marc potential attendance really 1/3 that of Joseph? And is Joseph's really 30% or might it be 25? Things happen when you reach large numbers that simply make 80% more valid than all this analysis. I just came back from a wedding. 550 invited. 452 attended. For purposes of planning the hall and starting to talk to the caterer, the initial estimate of 440 was fine.

Mat I offer a line from my toast to the couple? "Remember, if your wife is happy but you are not happy, you are still far happier than if your wife is unhappy, but you are happy."

For large numbers, 80% is what you'd expect. There are some situations that would make the numbers worse. For example, is Marc's potential attendance really 1/3 of Joseph's? And is Joseph's really 30%, or might it be 25%? Things happen when you reach large numbers that simply make 80% more valid than all this analysis. I just came back from a wedding. 550 invited. 452 attended. For purposes of planning the hall and starting to talk to the caterer, the initial estimate of 440 was fine.

May I offer a line from my toast to the couple? "Remember, if your wife is happy, but you are not happy, you are still far happier than if your wife is unhappy, but you are happy."