Hi this is dr. Vahid ariados and I’m delighted to demonstrate sampling sampling methods and the differences between samples and populations in this video. First of all. I would like to draw a difference to discuss the differences between samples and populations a population is a group of people. Pretty much like this group that you want to investigate for example all learners of English who are in a certain country or all Singaporeans secondary school students so this becomes your population now from this population. You need to draw a sample in research what is a sample, what is sampling in researchso those observations that you make from the population become your sample. Why do we do sampling. Because it’s a lot more convenient to have multiple observations from the SAP from the population rather than to go around and investigate everybody in that population. Because this is not very practical under many circumstances unless you have a huge amount of budget so samples are are a number of people or observations who or which have been drawn from a population through different approaches. The sample in research what is a sample, what is sampling in researchmust be representative of the population. If it’s not representative the results that you obtain from the sample in research what is a sample, what is sampling in researchcannot be extrapolated to the population so the results or your findings do not have generalizability. So what do we do in order to improve the generalizability of your findings that is how can we ascertain that. Your sample in research what is a sample, what is sampling in researchis representative of this larger population. Well that’s where the idea of sampling techniques comes into the picture there are different sampling techniques in this slide. I have presented five of them here. I think they’re most the most commonly used sampling techniques. I’m gonna present them in this order first. I will discuss this simple random sampling. The number two is stratified sampling or stratified random sampling followed by cluster sampling then systematic sampling and finally convenience sampling. It’s important to note that the samples representativeness of the population arguably decreases as you move from number one to number five.
But it might not always be so so. I’m gonna explain further and the following slides to see what I mean by that first of all a random sampling. Technique is a methodology in which each sample in research what is a sample, what is sampling in researchin the population has an equal probability of being chosen. Okay so let’s say you are this person here and there is a person who is far away from you in the population. You have the same chance or or probability of being chosen as a sample in research what is a sample, what is sampling in researchas this person has and as anybody else has in this sample. And that’s what makes it a random kind of sampling in order to do random sampling. The first thing you need to do is defining your population for example my population might be English learners who are based in China or Chinese as a second language learners who are in Singapore or who are in China or who live in Malaysia. For example some overseas students who are studying in. Malaysian are interested to learn Mandarin or Chinese after this we need to define a sampling frame and I would like to explain this a little bit because we hardly define this in second language research in research what is a sample, what is sampling in researchbut I think is a useful concept a sampling frame is a group of potential subjects. From which you draw your sample in research what is a sample, what is sampling in researcha sampling frame will be here right. It stands between your population and your sample in research what is a sample, what is sampling in researchso from the population you choose a sampling frame and then from the sampling frame. You choose your sample in research what is a sample, what is sampling in researchso this will be what you want. A sampling frame is useful. Because due to practicality reasons we don’t always have access to the entire population or if we do we can’t really do a very good random sampling because we don’t have budgets. That’s the question of practicality so it’s not plausible to randomly select a large number of people therefore we can confine our research in research what is a sample, what is sampling in researchpopulation to a sampling frame of people or students who are enrolled at our university or to universities so that becomes our sampling frame. Of course this will influence the representativeness of your sample in research what is a sample, what is sampling in researchbut under these circumstances and due to the practicality issues.
I think this is perhaps one of the best strategies that we can adopt in our research in research what is a sample, what is sampling in researchafter doing this. We create a list of members. Hopefully we can get a list of members from somewhere for example from some administration offices at our university or elsewhere if we have the list of the members it will be easy to assign numbers to those members then we should assign numbers for example we have 200 a list of 200 students. Then the numbers will will move from 1 to 200 following this. We can choose a sample in research what is a sample, what is sampling in researchsize because we need to look at the list and see how large that list is. We might decide that the entire list is gonna be invited to my study. So that’s one way of doing it or you might say from this sample in research what is a sample, what is sampling in researchfrom this list. I’m gonna choose a sample in research what is a sample, what is sampling in researchof 100 people that becomes my sample in research what is a sample, what is sampling in researchsize so in N equals 100. This sample in research what is a sample, what is sampling in researchof 100 people should be drawn randomly using a kind of for example software package like SPSS or other software packages which can help you do that. Kind of random selection if random selection is not a possibility. Or if you think it doesn’t work for you due to some reasons which I will explain you stratified. Random sampling is another option for you in a stratified. Lant random sampling. You divide the population. Let’s say this is your population into n separate strata. So this is stratum 1. This is actually stratum. It shouldn’t be strata stratum one stratum 2 and stratum 3 note that members of each stratum have the same features for example. If if just let’s pretend that we only have two oops – gender groups Group one and let me just choose a different college group – so this is male or female or female or male doesn’t really matter. Let’s pretend that we don’t have this for a minute. Just ignore this please. What happens is all people in this sub sample in research what is a sample, what is sampling in researchor this sorry this stratum are all males or females similarly in this stratum. People should have the same feature.
There are either old males or old females. Why do we do this because this is especially important when the number of subjects in each strata is not equal across those strata. So then everybody here will be assigned as the same chance of being selected in our sample in research what is a sample, what is sampling in researchand same here and same here. Another example would be that you have three classes of socioeconomic backgrounds socioeconomic status. This is class one. Whatever that class is this is class two and this is class three. Then you’ll have three strata from each of these strata. You will select a representative number of people representative to extend that you do the random sampling on each of the strata. This is about a stratified random sampling. The other kind of sampling as I mentioned before is cluster sampling in cluster sampling. Basically the population is divided into unequal stirrers for example towels in a province etc. Now let’s pretend that these clusters are unequal. Forget about the fact that they have three numbers with the three characters in each cluster. So we’ve got one two three four five clusters and each of them could be representative of a town or a city in a province etc. Then samples are randomly selected from the clusters from this cluster. One sample in research what is a sample, what is sampling in researchwill be randomly selected and another one from this and yet another one from this and another one from this cluster. And finally one from this cluster. So you’re gonna have five different. Clusters with five randomly selected samples from each and those five randomly. Selected samples will become our sample. I would like to elaborate further about this Kyah technique because it can be divided into a one-stage clustering sample in research what is a sample, what is sampling in researchand cluster sampling or two-stage or multiple stages. This is a very interesting figure from this website by the way if you have noticed. I have provided the list of all web sites from which I’ve gotten the figures in case you would like to check on your own. Feel free to go ahead.
I’ll also provide the addresses. The website addresses at the bottom of this video. So in a multi-stage cluster sampling in this figure. In a multi-stage cluster sampling. We have gone through four stages for example in a country as vast as the United States. We cannot investigate every person in every state therefore let’s say the question is whether English as a second language learners progress over time after they study English in America. Progress over time progress in their reading comprehension for example or speaking skills or not your question is about. ESL learners in America and that’s really a very large large population therefore it’s recommended that in the first stage you randomly select States here. We have selected seven states in the second stage you randomly select cities towns counties and counties within each of those states so this kind of sampling is going to be done on each of these states. So here here here in on this states on this this states and this one and this state so as you see there are seven states. Stage three includes the random selection of schools within each city or each town or each county within this or this each of them. Actually the same thing happens and in the final stage you’re gonna randomly select students within each school here yes. Gary the final stage. This is quite more convenient and gives you a chance to have a representative sample in research what is a sample, what is sampling in researcha relatively representative sample in research what is a sample, what is sampling in researchof a large population as large as a country like the United States of America the other technique of sampling is called systematic sampling a systematic sampling gives you a chance to choose every case subject to be a part of the sample in research what is a sample, what is sampling in researchfor example. Here we’ve got every third subject so. I simply say 1 1 the 1 is missing in the figure but 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 and it goes on and on it’s gonna be case subject selected to be a part of the sample in research what is a sample, what is sampling in researchin order to do the systematic kind of sampling. First of all what we need to do is to create a list.
For every member of the population and then choose the member choose the members at a predefined regular interval which was 3 in this example. It doesn’t have to be 3. Always it depends on your sample in research what is a sample, what is sampling in researchsize and so on and so forth ok and the the final the the last type of systematic sorry of sampling. It’s called convenient sampling. It’s called convenience because samples. Come from the most available group not necessarily the representative group if this is your population the most available group this is you researcher. The researcher right this person with a circle around you the most available population or the sample in research what is a sample, what is sampling in researcharound you are these guys these three so it’s convenient really to ask them to participate in your study but then what about these people who are far away from you and not are not available. They will not get a chance to be a part of the sample in research what is a sample, what is sampling in researchand the inclusion or exclusion of such. These people might have a significant impact on your results if I totally get a different profile in your research in research what is a sample, what is sampling in researchand that might not be generalizable to the sample in research what is a sample, what is sampling in researchto the population from which the sample in research what is a sample, what is sampling in researchhas been drawn therefore one of the limitations of this kind of research in research what is a sample, what is sampling in researchis the fact that the is a higher probability of getting a biased sample in research what is a sample, what is sampling in researchand therefore we must. We must make sure that we do not over claim our findings when we have got a convenient sampling. There are two things that are recommended to be done in research in research what is a sample, what is sampling in researchbut honestly. I haven’t seen this much in published research in research what is a sample, what is sampling in researchin second language learning and even language assessment. I myself am guilty of at least one of them. The first one is describe the sample in research what is a sample, what is sampling in researchvery carefully so that the reader will know how generalizable to your results are. It’s a description as much as you can and also under the limitation of the study. Do make sure to acknowledge the limitation in the form of a sentence like this. The findings are true for the sample in research what is a sample, what is sampling in researchof the study and might hold in a general population mic.
Actually this there’s a little bit of typo here. I mean I should have written. Might not hold okay. That’s just a correction. Might not hold. In a general population. Further studies should investigate whether the results can extrapolate to a population as a similar sentence. Similar to this would be useful so there your reviewers and also your readers will know how much your your sample. I mean your results are generalizable to a population and future. Researchers are also aware that there is a limitation in your study that they can address. Well that’s the end of this video. Thank you very much for your attention and if you liked the video please give it a like and subscribe to the channel. Have a good day.
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