An exercise : A quality control engineer gets 1000 items. How big a sample will he require to say that the he is 95% confident that the sample represents the population?? Is this possible to answer without knowing anything else?? All examples that I have seen so far work with either certain values and/or known standard deviation and certain samples.
My question basically is: is Cochran's formula enough / suitable if I want to determine minimum sample size to examine in order to get confidence about the whole population? Lets say I have a batch of 1000 phones. I cannot test all of them but I need to test enough of them to be somehow confident that the whole population has the same property (e.g. simply is working). This Cochran's formula seems to be exactly what I need but I am not sure.
Can Cochran's formula be used here?
