Hate this is stopped and cons of number nine population versus the sample or populations and samples to start on the business real to a page of statistics to the statistics revealed a look tonight's presentation from the SOM Department. And we will skip to almost all the way again on to two page to PowerPoint slide number 1:01 a.m. and that talks about the populations versus samples now this is an important topic, because is a. We need to know conceptually, what kind of data were looking at whether or not we're looking at something like sample, which is he usually the case or the population in the pocket or of which usually not the case of the population is everything in the universe in a particular environment of the population of all students at Dell state or search the population of all students in the sea issue system. The population of all the envelopes in a particular office of the population of all the envelopes in the world to, you need to know what population are talking about, and when you looking at a sample of numbers, are you looking at a digicam out all the envelopes in the world or just the envelopes in your particular office for example is the other reason this is important is practical matters, because you can get the calculations right in the denominator for example in the variants which which affects the standard deviation unless you know whether or not you dealing with a population sometimes called the end method or the sample sometimes called the 10 minus one method to really subtract 11 were in the denominator were more working with the sample on redoing the various calculations and tank to the next light is a couple of things about the population population as I said this bullet point number one is a collection of all items per example all the life bolts made at a factory that can be a population if you do find it that way and when we talking about poor populations were talking about particular measures like a means and standard deviations and proportions would call those parameters easy to remember because P. and population does look he has a parameter. We also tend to use uppercase letters like uppercase scam and we tend the use Greek letter and in general, like a signal off for a lowercase sigma for to and standard deviation for sample invariance of the variants with the standard would be Sigma squared for sample soap population parameters is a measure of the population. Number one population mean, for example that's the average number of hours in the life of all pull its same as the population mean for the population average if your world although average isn't the best word to you as a member to us the population proportion that would be the percentage of all bull's letter to factor for example lets a measure of a proper particular proportion and when that's not listed here could be the population variance with a population standard deviation and.
Is a sample to sample as of the first bullet said is part of a population of some people would argue that we can't see the whole population, which can only see sample we can never really ever get to the entire population. So most of the time, what we have is the sample in the problem wool on the exam will always state that if it doesn't stay to issue probably assume that if the sample in our population. So for example part of a population would be just the bolts tested via a particular inspector at the factory and not all the bolts just up some ball and hopefully that sample is representative of the entire population of and the answer we have to use good sampling strategy social talk about later to be able to make sure that that's sure to call fully if we were to take other samples using the same kind of sampling technique we would get similar results to what we're seeing now, what would it to the measures that we compute now for this particular sample. Just as we talk about parameters. Of e with populations we talk about statistics that go was samples and I know the word statistic use use to a lot of different ways are several different ways, but here statistic means a measure of the sample justice of the second bullet points as a assist to stick as a measure of a sample that's an estimate of a parameter to remember we can as we can only estimate the parameter because we can't normally see the population. We usually can't measure the entire population, which means we can measure the parameter of the population parameters correctly for or are accurately all we can do is estimate the population parameter with a a particular sample statistic like we such as we estimate the population mean with the sample statistic the sample mean, we estimate of the population parameters with sample statistics to hear a couple of examples number one in the sample mean purchase the average hour number of hours in the lightbulbs in the tested by an inspector so that sounds similar to what we did before, but it's not just the average number of hours just in the light olds tested by the inspector which isn't all of the bulbs why can't the inspector test all of the ball is probably too expensive to test all the balls we just want to test the sample and see if there's any deviation from what we expect in terms of quality for example number two is a sample proportion options for sample the percentage of all the bull is in the sample of her defective opinion, not the percentage of the balls in the entire factory just in that particular sample artifact of. So that's the difference between populations and sample and it always have to be cognizant as to which one you are dealing with