Questions about statistics What can we tell from the change of the normal curve (including the width,the height) For the biased sample,we got two types.One is the convenience sample,and the other is the voluntary response sample.For t

Questions about statistics What can we tell from the change of the normal curve (including the width,the height) For the biased sample,we got two types.One is the convenience sample,and the other is the voluntary response sample.For t
Questions about statistics
 What can we tell from the change of the normal curve (including the width,the height)
 For the biased sample,we got two types.One is the convenience sample,and the other is the voluntary response sample.For the voluntary response sample,we got also two types:call-in polls & voting on-line.So my questions are:1) we got other ways to volunteer,so is there any typically types of voluntary sample or how can we know the sample types of these volunteering which is not by the call-in and the on-line?2) if I am just waiting in a stationary space having a investigation,is the samples I got a convenience sample?If so,how to explain that to get these samples,there must be people coming by voluntary join the investigation,so why is this not a voluntary sample?3) When we are having these typical problems like the one above,there sometimes are people who joined the investigation not because they are volunteering to do so,but because they want to finish listening to those recommendations (people will always recommend others to join the investigation),are those still voluntary?So then this voluntary sample is not those people who really volunteer but is totally are the people joining,is it?
 How do you get the confidence levels are 90%,95%,and 99%?Why not others?And how do you know that 95% of the sample means from the population must be within 1.96 standard deviation of the population of the population mean?Why we just don’t use those 34%,95%,and 99.7%?What is the different between these two?And why we need the standard deviation,what can it represent?And for the population and the sample,I think we can’t tell exactly the sample is.For example,they give you a whole school’s sample,is it a population?If so,what about all the schools over the town,the province,the country,the world,even the whole universe?And what about including colleges,including universities,including the companies… I know what I think is a little bit crazy,but what about a class,a group,etc,can they be a population,or,they must be a sample.So mainly,my question is what is the confines of population and sample,do they really have a limit,if don’t,how can I recognize them?
 Why we are learning about the binomial experiment and the approximately binomial experiment?What do they mean,what can they show and what are they created for?
 How to get below these formulas:Why is different from other standard deviation?
还有一些统计问题：

Questions about statistics What can we tell from the change of the normal curve (including the width,the height) For the biased sample,we got two types.One is the convenience sample,and the other is the voluntary response sample.For t
you can get the answers just from below these webseides:
http://140.127.187.205/cllang/%A6%DB%BDs/ProbabilityStatistics/2.4BernoulliTrialAndBinomialDistribution.pdf