Follow Anna’s Why would you? advice. The point is simply to have a reliable computation performed on the observations, and you do whatever is equivalent to that.
If the opinion involves a computation from the information source that is difficult enough that people might do it wrong, then count more sources as more evidence. After a math exam, when you poll your friends,
“Who answered pi for number 6?”,
it is rational to be more confident in “pi” as more of your computationally skilled friends answer “pi”, even though it all came from the same information: the exam question. This is similar to the phenomenon that checking over your own workings should typically make you more confident, depending on how complex they are.
Another sort of such a computation is memory itself. Some people fail to compute the correct present memories from their past exposure to stimuli. So if you want to know
“Was there a red card in the parking lot?”,
more witnesses should make you more convinced, even if they’re all honest people… they might just have bad memories.
But if you have 3 friends standing in your dining room right now, and you ask them
“Are there enough chairs in there for all 4 of us?”,
and someone says “yes”, additional yesses should contribute very little marginal confidence. In summary,
Extra opinions on the same information are redundant only insofar as computational error checking is redundant.
It matters how confident you are in the original information source, and how confident you are that it was relayed properly. Suppose the question you is “Will it rain tomorrow?” In the first scenario, you ask some people, and each one pulls out their phone, looks at it, and says “weather.com says yes”. In this case, the probability that it will rain is almost exactly equal to the accuracy of the original information source, and the additional opinions add nothing. In the second scenario, you ask some people, and each of them says “I checked weather.com’s forecast this morning, and I think it said yes.” In this case, your estimate of the probability that it will rain is a bit lower, because they might have mis-remembered the forecast; but as you ask more people, your estimate should increase asymptotically towards your estimate of the forecast’s accuracy.
Follow Anna’s Why would you? advice. The point is simply to have a reliable computation performed on the observations, and you do whatever is equivalent to that.
If the opinion involves a computation from the information source that is difficult enough that people might do it wrong, then count more sources as more evidence. After a math exam, when you poll your friends,
“Who answered pi for number 6?”,
it is rational to be more confident in “pi” as more of your computationally skilled friends answer “pi”, even though it all came from the same information: the exam question. This is similar to the phenomenon that checking over your own workings should typically make you more confident, depending on how complex they are.
Another sort of such a computation is memory itself. Some people fail to compute the correct present memories from their past exposure to stimuli. So if you want to know
“Was there a red card in the parking lot?”,
more witnesses should make you more convinced, even if they’re all honest people… they might just have bad memories.
But if you have 3 friends standing in your dining room right now, and you ask them
“Are there enough chairs in there for all 4 of us?”,
and someone says “yes”, additional yesses should contribute very little marginal confidence. In summary,
Extra opinions on the same information are redundant only insofar as computational error checking is redundant.
It matters how confident you are in the original information source, and how confident you are that it was relayed properly. Suppose the question you is “Will it rain tomorrow?” In the first scenario, you ask some people, and each one pulls out their phone, looks at it, and says “weather.com says yes”. In this case, the probability that it will rain is almost exactly equal to the accuracy of the original information source, and the additional opinions add nothing. In the second scenario, you ask some people, and each of them says “I checked weather.com’s forecast this morning, and I think it said yes.” In this case, your estimate of the probability that it will rain is a bit lower, because they might have mis-remembered the forecast; but as you ask more people, your estimate should increase asymptotically towards your estimate of the forecast’s accuracy.