![]() ![]() The simple random sample, you can stratify, or So, once again, these areĪll forms of random surveys, or random samples, you have We are sampling from the clusters, but then we're gonna survey every single person inĮach of these clusters, every single person in Get good representation, but we are still sampling, Sample, because we're going to randomly sample ourĬlassrooms, each of which have a close or maybe a exactīalance of males and females so we know that we're gonna Sample the actual classrooms, so that's why it's calledĬluster, or cluster technique, or clustered random Have an even distribution of males and females, or prettyĬlose to even distributions. Just say that we can split, let's say we can split our population into groups, maybe these are classrooms, and each of these classrooms So, for example, we might, instead of sampling individualsįrom the entire population, we might say, look, you know, on Tuesdays and Thursdays, and this, well, even there as you can tell this is not a trivial thing to do, let's Each of those groups we feel confident has a good balance of male females. Over here, clustered, a clustered sample, and what And so what you might say is, well, you know what I'm gonna do? I'm going to, there's a techniqueĬalled a clustered sample. There's disproportionately male or disproportionately female. Random people, it's very likely that it's close toĥ0/50, but there's some chance, just due to randomness, Males and females in the school, and there is some probability, you know, if I do 100 Issue where you say, well, I'm actually moreĬoncerned that we have accurate representation of And so that makes sure that you are getting indicative responses from at least all of the different age groups or levels within your university. Juniors, and seniors, and instead of just samplingġ00 out of the entire pool, we sample 25 from each of these. So we'll stratify it byįreshmen, sophomores, juniors, and seniors, and then we sample 25 from each of these groups. We get a appropriate sample of freshmen, sophomores, Population, I'll draw it as a square here just for convenience, and we're gonna stratify it by, let's say we're concerned that Take that same population, we take that same Taking our entire population and essentially stratifying it. There are other techniques at our disposal. Taking a simple random sample that is truly random, onceĪgain, it's some probability that it's not indicative Number of engineering majors versus English majors,Īnd that's a possibility. Number of boys over girls, or a disproportionate number of freshmen, or a disproportionate Just happened to select maybe a disproportionate Sample, but there is some probability that, just by chance, your random number generator Unlikely that you're going to have bias from this That is allowing us to pick the students. We have a string of numbers or something like that, Know it's random because a random number generator, or ![]() We are just randomly picking people out, and we Whole population and randomly, let me just draw this. Sample of 100 students, that I'm going to apply the survey to, so that would be a simple random sample. So, simple, simple, random, random, sample, and this is saying, alright, let me maybe assign a number toĮvery person in the school, maybe they already haveĪ student ID number, and I'm just going to get a computer, a random number generator, to generate the 100 people, the 100 students, so let's say there's a You actually get down to it, it's not always as straightforwardĪs you would think. Pretty straightforward to do a random sample, but when So our sample could either be random, random, or not random. It being indicative of the entire population, we want Now in order to avoid having bias in our response, in order for it to have the best chance of Sample this population to get an indication of how Let's say we're a college and there's 10,000 people in the college. ![]() One option is to just go toĮvery member of the population, but let's just say it'sĪ really large school. Who are we going to get to actually answer this survey. Quality of math instruction at the school, so we construct a survey, and we just need to decide And we want to get a sense of how these students feel about the Say that we run a school and in that school there is a population of students right over here.
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