In stratified sampling, the study population is divided into nonoverlapping strata, and samples are selected independently from each stratum. Maths revision video and notes on the topic of stratified sampling. Aug 24, 2012 this video explains stratified sampling. Final members for research are randomly chosen from the various strata which leads to cost reduction and improved response efficiency. As this method provides greater precision, greater level of accuracy can be achieved even by using small size of samples. Covers all parts of the gcse syllabus, including sampling methods random and stratified sampling. Random sampling random sampling is a method that, in a population, every element has a chance to be included in a sample.
Stratified sampling the stratum weight, h, is the probability that a randomly selected unit belongs to stratum h, i. Stratified sampling is a sampling technique where the researcher divides or stratifies the target group into sections, each representing a key group or characteristic that should be present in the final sample. Simple random sampling samples randomly within the whole population, that is, there is only one group. If the groups are of different sizes, the number of items selected from. See bankier 1988 for more details about the sample size allocation. Full stratified sampling lesson if youre still planning on teaching stratified sampling, this detailed lesson includes increasingly difficult examples to get students thinking. Feb 02, 2015 presentation on stratified sampling 1.
The school is the cluster with the children being selected randomly from within the cluster. Understanding stratified samples and how to make them. Gcse revision video 31 stratified sampling youtube. The only sampling is simple random sampling of census tracts within strata.
This sampling method is also called random quota sampling. Disadvantages advantages stratified sampling requires more administrative effort than simple random sampling considering the additional division of samples based on characteristics can provide greater accuracy smaller and more accurate samples can be used this is used when. In stratified sampling, we split the population into nonoverlapping groups or strata e. Random and stratified sampling this lesson can be used for revision for the higher maths gcse. A teacher wants a sample of 50 people from a school. Disproportionate stratified sampling takes a different proportion from different strata. Random and stratified sampling questions, worksheets, videos. Stratification is the process of dividing members of the population into homogeneous subgroups before sampling. In a random sample, every person in the population has the same chance of being selected.
As learning progresses students are challenged to work the problem in reverse by finding the population of each strata given the sampling size. Stratified sampling is a method we can use to make our sample more representative. Samples are then pulled from these strata, and analysis is performed to make inferences about the greater population of interest. Sampling theory chapter 4 stratified sampling shalabh, iit kanpur page 2 notations. May 10, 2014 gcse revision video 31 stratified sampling. The examples are quick and concise with exam style questions, go to gcse maths if you need more indepth explanations. In stratified sampling, the population is partitioned into nonoverlapping groups, called strata and a sample is selected by some design within each stratum. Stratified sampling is a method of sampling from a population. Estimation of population mean under stratified random sampling note that the population mean is given by x h l h h h l h n i hi l h w x n x h.
Given an array and a number of samples to generate, randomstrat fills in all or part of the array with stratified random samples. Number of sampling units to be drawn from ith stratum. This is where we divide the population into groups by some characteristic such as age or occupation or gender. Stratified random sampling an appropriate group is decided upon i. Choose a random sample from each of the subgroups that were stratified. The resource would also be suitable as hand out notes for. Stratified random sampling divides a population into subgroups or strata, and random samples are taken, in proportion to the population, from each of the strata created.
Jan 27, 2020 a stratified sample can also be smaller in size than simple random samples, which can save a lot of time, money, and effort for the researchers. The concept of having a representative leads to random sampling. Feb 15, 2009 stratified random sampling slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. When a population is divided up into groups, taking a stratified sample ensures that each group is asked in the correct proportion. The population is classified by age as shown in the table below. Stratified sampling statistics gcse 91 teaching resources. Stratified sampling gcse full lesson teaching resources.
This may be done to ensure minorities are adequately covered. For example, an urban ward may contain 8 deprived wards and 2 undeprived wards. Stratified sampling definition of stratified sampling by. This resource is a complete lesson and ready to teach. Statisticians attempt for the samples to represent the population in question. Total sample size k i i nn population n units stratum 1. The aim of sampling is to select a sample which is representative of the population.
Stratified random sampling is a type of probability sampling using which researchers can divide the entire population into numerous nonoverlapping, homogeneous strata. Stratified sampling deals mainly with fractions and is usually on a gcse calculator question paper. Stratified sample by brianna mccreadybranch on prezi. For example, suppose you want to know about reading habits in the uk. I hope the video helps and please do leave a comment thanks. Stratified sampling for oversampling small subpopulations. Ppt stratified sampling powerpoint presentation free. In a stratified sample, a proportionate number of measurements are taken is taken from each group. I am struggling to create a stratified sample of size 100 using stratified random sampling with 3078 observations. Stratified random sampling helps minimizing the biasness in selecting the samples.
Proportionate allocation uses a sampling fraction in each of the strata that is proportional to that of the total population. Divide the population into the subgroups so that the subgroup will be homogeneous. This website and its content is subject to our terms and conditions. Date published september 19, 2019 by shona mccombes. Stratified sampling is sometimes called quota sampling or stratified random sampling.
Stratified sampling practice questions corbettmaths. Stratified random sampling definition investopedia. In statistics, quality assurance, and survey methodology, sampling is the selection of a subset a statistical sample of individuals from within a statistical population to estimate characteristics of the whole population. Two advantages of sampling are lower cost and faster data collection than. Stratified random sampling ensures that no any section of the population are underrepresented or overrepresented. In choicebased sampling, 7 the data are stratified on the target and a sample is taken from each stratum so that the rare target class will be more represented in the sample. Lesson includes definition and builds the difficulty of examples which my class found insightful.
Similar to stratified sampling but the groups are selected for their geographical location. Proportionate stratified sampling in this the number of units selected from each stratum is proportionate to the share of stratum in the population e. Tes global ltd is registered in england company no 02017289 with its registered office at 26 red lion square london wc1r 4hq. Sampling is the process of looking at a small selection of peopleobjects from a wider population in order to learn new information about that population. By separating the population into groups age groups, genders, etc. The purpose is to ensure adequate representation of subjects in each stratum. Stratified sampling is a probability sampling technique wherein the researcher divides the entire population into different subgroups or strata, then randomly selects the final subjects proportionally from the different strata. Then the members for the sample are chosen from these individuals, of course in.
Take observations along a line, like up a beach from sea shore to base of the cliffs. Ppt stratified sampling powerpoint presentation free to. The researcher identifies the different types of people that make up the target population and works out the proportions needed for the sample to be representative. When you conduct research about a group of people, its rarely possible to collect data from every person in that group. Stratified sampling questions worksheets and revision mme. Stratified sampling is a type of sampling method in which the total population is divided into smaller groups or strata to complete the sampling process. Stratified random sampling is a better method than simple random sampling. In statistical surveys, when subpopulation within an overall population vary, it is advantageous to sample each subpopulation stratum independently. A sample is a method of survey that takes a representative of the population. The strata are regions, fixed in advance, not sampled. Random and stratified sampling questions, worksheets. Stratified sampling divides your population into groups and then samples randomly within groups. To summarize, one good reason to use stratified sampling is if you believe that the subgroup you want to study is a small proportion of the population, and sample a disproportionately high number of subjects from this subgroup.
The sample is the group of individuals who will actually participate in the research. Stratified sampling is a probability sampling method and a form of random sampling in which the population is divided into two or more groups strata according to one or more common attributes. In order to fully understand stratified sampling, its important to be. The members in each of the stratum formed have similar attributes and characteristics. For example, if a class has 20 students, 18 male and 2 female, and a researcher wanted a sample of 10, the sample would consist of 9 randomly chosen males and 1 randomly chosen. This lesson can be used for revision for the higher maths gcse. Definition of stratified sampling a stratified sample is a probability sampling technique in which the researcher divides the entire target population into different subgroups, or strata, and then randomly selects the final subjects proportionally from the different strata. A stratified sample can also be smaller in size than simple random samples, which can save a lot of time, money, and effort for the researchers.
Stratified sampling simple random sampling means that each record in the population has the same chance of being selected. Choicebased sampling is one of the stratified sampling strategies. Stratified sampling textbook exercise corbettmaths. Hence, there is a same sampling fraction between the strata.
Accordingly, application of stratified sampling method involves dividing. Sampling techniques matchup use this simple activity to start a discussion about the merits of various sampling techniques relative to given situations. This is when the population is split into could have sub groups. A random sample may by chance miss all the undeprived areas. In stratified random sampling or stratification, the strata. Stratified sampling a random sample from a homogeneous subgroup a.
The strata is formed based on some common characteristics in the population data. Number of sampling units in ith strata 1 k i i nn ni. Take observations at individual points, like separate houses on a street. Students learn the difference between different types of sampling methods and how to calculate a stratified sample size using equal proportions. A simple random sample of students was selected from each grade. The conditions the stratified random sampling have to meet are. Stratified random sampling intends to guarantee that the sample represents specific subgroups or strata. What is the difference between simple and stratified random. For taking random samples of an area, use a random number table or random number generator to select numbers. This will enable you to compare your subgroup with the rest of the population with greater accuracy, and at lower cost. To do this, you might ask 500 people from the uk how many books they finished last year this is a sample.
This is where each member of the population is equally likely to be included. Complete stratified sampling lesson made for my year 10, top set, gcse class. After dividing the population into strata, the researcher randomly selects the sample proportionally. Edexcel gcse mathematics linear 1ma0 stratified sampling materials required for examination items included with question papers ruler graduated in centimetres and nil millimetres, protractor, compasses, pen, hb pencil, eraser. A powerpoint math or maths presentation on stratified. Then make sure our survey includes people from each group in proportion to how many there are in the whole population. For example, geographical regions can be stratified into similar regions by means of some known variable such as habitat type, elevation or soil type. Stratified sampling module 3 session 6 session objectives to introduce basic sampling concepts in stratified sampling demonstrate how to select a random sample using. Stratified sampling is used to select a sample that is representative of different groups.
Previous rounding highest lowest practice questions. We look at the idea that stratified random sampling can be used where the population under consideration separates naturally into subgroups or strata and that numbers taken in each of these samples. Stratified sampling in this method, we divide the population into smaller units. Stratified sampling would take into account the proportional area of each habitat type within the woodland and then each could be sampled accordingly. Calculate the number of people that should be sampled from each age. In this method, the elements from each stratum is selected in proportion to the size of the strata. Stratified random sampling is a method of sampling that involves the division of a population into smaller subgroups known as strata. Sampling over space three strategies for area sampling. Sampling ppt free download as powerpoint presentation. This is because this type of sampling technique has a high statistical precision compared to simple random sampling. Proportionate stratified sampling takes the same proportion sample fraction from each stratum. Sampling ppt stratified sampling sampling statistics. If you do this, and want to make an estimate about the population, you will have to weight within. Presentation on stratified sampling linkedin slideshare.
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