In systematic random sampling, the researcher first randomly picks the first item or subject from the population. Jan 06, 2016 gcse mathematics stratified sampling questions appear on many exam papers and you can download the questions here. Stratified random sampling intends to guarantee that the sample represents specific subgroups or strata. Stratified sampling worksheet and exam practice qs.
Random and stratified sampling this lesson can be used for revision for the higher maths gcse. Selecting a stratified sample with proc surveyselect. Stratified random sampling intends to guarantee that the sample. Random sampling, stratified sampling, systematic sampling. Apart from that, the statistical analyses used in the case of cluster sampling are also more complex than the ones used in case of stratified sampling. In a biased sample, some elements of the population are less likely to be included than others. Ppt stratified sampling powerpoint presentation free. The table shows the number of each type of worker in the factory. Simple random sampling and systematic sampling simple random sampling and systematic sampling provide the foundation for almost all of the more complex sampling designs based on probability sampling. 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. The estimate for mean and total are provided when the sampling scheme is stratified sampling. We will compare systematic random samples with simple random samples. Random and stratified sampling questions, worksheets.
A random sample is taken from particular social categories, e. Every fifth person boarding a plane is searched thoroughly. This can be seen when comparing two types of random samples. Households may be randomly selected from a random sample of streets from a random selection of areas. Stratified sampling higher collecting data ccea gcse. Jenny is carrying out a survey for her gcse mathematics project. The most representative samples from this method are achieved when the sampling frame list is randomised this is known as systematic random sampling. What is the purpose of stratified systematic sampling. Gcse statistics revision notes collecting data sample this is. There are three methods of sampling to help overcome bias.
Selecting a sample stratified 2 12d pilot survey 2 12e biased questions 1. A simple random sample is used to represent the entire data population. Stratified systematic sampling regular samples are taken from within certain categories. Gcse maths alevel maths gcse to alevel pure maths statistics mechanics alevel maths. However, the difference between these types of samples is subtle and easy to overlook. It is possible to combine stratified sampling with random and systematic sampling. 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. The most common purpose for stratified sampling is to make the sample more representative of the population. Apr 19, 2019 simple random samples and stratified random samples are both statistical measurement tools. Sample this is when data is collected from part of the population. The examples are quick and concise with exam style questions, go to gcse maths if. Calculate the number of people that should be sampled from each age. Cluster random sampling is one of many methods used to gain information about a population.
For example, an urban ward may contain 8 deprived super output areas and 2 undeprived super output areas. Three techniques are typically used in carrying out step 6. Whether you want a homework, some cover work, or a lovely bit of extra practise, this is the place for you. Stratified random sampling can be tedious and time consuming job to those who are not keen towards handling such data. The pupil committee of 30 pupils is selected using a gender stratified sample. Systematic random sampling1 each element has an equal probability of selection, but combinations of elements have different probabilities. Data collection and sampling edexcel gcse geography revision. Stratified random sampling requires more administrative works as compared with simple random sampling. I can see the advantages of stratified random samples, as it is easier to sample smaller classes as well. A comparison of systematic versus stratified random sampling design for gradient analyses. At a local community college, five math classes are randomly selected out of. Pdf a comparison of systematic versus stratifiedrandom. There are 10 boys and 20 girls on the school committee. By contrast, with a stratified sample, you can make sure that 80% of your samples are taken in the deprived areas and 20% in the undeprived areas.
Home stratified sampling method stratified sampling method 380. We will examine simple random sampling that can be used for sampling persons or records, cluster sampling that can be used to sample groups of persons or records or networks, stratification which can be applied to simple random and cluster samples, systematic selection, and stratified. Jan 06, 2016 this video is all about gcse mathematics stratified sampling and forms part of the playlist gcse stratified sampling the question deals with. If the groups are of different sizes, the number of items selected from each. In the selection of a sample, a current practice is to define a sampling design stratified on subpopulations. Also, by allowing different sampling method for different strata, we have more. Updated for the 2012 exam ultimate gcse statistics. May 08, 2019 systematic sampling is simpler and more straightforward than random sampling. Gcse revision video 31 stratified sampling youtube. Systematic sample such as every 4th stratified sample randomly, but in ratio to group size cluster sample choose whole groups randomly random sampling. Considering the set up of stratified sample in the set up of a systematic sample, we have number of strata n. Sampling theory chapter 11 systematic sampling shalabh, iit kanpur page 7 recall that in the case of stratified sampling with k strata, the stratum mean 1 1 k stjj j yny n is an unbiased estimator of the population mean.
Introduction to stratified, cluster, systematic, and convenience. To obtain estimators of low variance, the population must be partitioned into primary sampling unit clusters in such a way that 157 7. Stratified sampling gcse full lesson teaching resources. Gcse revision video 31 stratified sampling duration. Population size n, desired sample size n, sampling interval knn. In geography fieldwork, times of day, week and year, the choice of locations to collect data, and the weather can all lead to bias. Sampling alevel maths statistics revision, topics include. Gcse statistics revision guide updated for the 2012 exam. If the population of nnk units is divided into n strata and suppose one unit is randomly drawn from each of the strata. To do this, you might ask 500 people from the uk how many books they finished last year this is a sample. Calculate the number of each type of worker that should be chosen. Stratified random sampling is a method of sampling that involves the division of a population into smaller groups known as strata.
Printerfriendly version reading assignment for lesson 6. A simple random sample and a systematic random sample are two different types of sampling techniques. Here only the first sampling unit is selected at random and the remaining units are automatically selected in a definite sequence at equal intervals. Stratified sampling module 3 session 6 session objectives to introduce basic sampling concepts in stratified sampling demonstrate how to select a random sample using. Data collection sheets should have a simple design so that the results are clear to read. For example, suppose you want to know about reading habits in the uk. This reduces the variance of the horvitzthompson estimator in comparison with direct. Stratified sampling higher collecting data ccea gcse maths. Whats the difference between stratified and systematic sampling. Systematic sampling is simpler and more straightforward than random sampling.
Stratified sampling is used to select a sample that is representative of different groups. The population is classified by age as shown in the table below. They can be a little challenging and please do practice all of the problems. Systematic sampling is a random sampling technique which is frequently chosen by researchers for its simplicity and its periodic quality. Sampling methods answers identify the sampling method. This approach is ideal only if the characteristic of interest is distributed homogeneously across. If the groups are of different sizes, the number of items selected from each group will be proportional. First, we need to establish how many people were at the convention. Random and stratified sampling questions, worksheets, videos. Check that you know the total population size this. A random sample may by chance miss all the undeprived areas.
In stratified sampling, we divide the population into nonoverlapping subgroups called strata and then use simple random sampling method to select a proportionate number of individuals from each strata. Systematic sampling is used where the study area includes an environmental gradient. What is the difference between systematic sampling and. The procedure involved in systematic random sampling is very easy and can be done manually. May 10, 2014 gcse revision video 31 stratified sampling. In this method, we divide the population into smaller units. This website and its content is subject to our terms and conditions.
Proportional stratified sampling pdf stratified sampling offers significant improvement to simple random. Tes global ltd is registered in england company no 02017289 with its registered office. 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. Stratified sampling an important objective in any estimation problem is to obtain an estimator of a population parameter which can take care of the salient features of the population. Megans systematic sample can begin with any number as long as the numbers that come after it are equally spaced. Suppose a population is composed 50% of men and 50% of women, and you expect they will give significa. Systematic sampling has slightly variation from simple random sampling.
The sample of people surveyed not a random sample of the whole population a stratified sample always considers proportions according to given criteria. The nth number is selected by dividing the target population size the number in the sampling frame by the desired sample size. Systematic sampling and stratified sampling are the types of probability sampling design. Tes global ltd is registered in england company no 02017289 with its registered office at 26 red lion square london wc1r 4hq. Then the members for the sample are chosen from these individuals, of course in. For example, if vegetation cover in an area of heathland is 60% heather and 40% gorse, for a stratified sample take 60% of the samples from within heather and 40% of the samples from within gorse. A free powerpoint ppt presentation displayed as a flash slide show on id. What are the disadvantages of stratified random sample. Here only the first sampling unit is selected at random and the remaining units are automatically selected in a. If the groups are of different sizes, the number of items selected from. Stratified sampling questions worksheets and revision mme. Select a sample stratified by one category and by more than one category. Calculate how many people she will need to sample from each age group. She uses a stratified sample of 60 students according to year group.
Complete stratified sampling lesson made for my year 10, top set, gcse class. It is sometimes hard to classify each kind of population into clearly distinguished classes. Then, the researcher will select each nth subject from the list. Systematic sampling selects every nth observation in a list e. In a random sample, each member of the population is equally likely to be included in the sample. They are also usually the easiest designs to implement. The examples are quick and concise with exam style questions, go to gcse maths if you need more indepth explanations. In a systematic sample, measurements are taken at regular intervals, e. It can also be more conducive to covering a wide study area.
A telephone survey is carried out to find which political party people support. Fabine wants to take a stratified sample of the visitors at the convention. We can also get more precise estimation by changing the sampling scheme. On the other hand, systematic sampling introduces certain.
Predictions for gcse edexcel maths calculator paper stats help gcse s1 question help with gcse stats coursework plan systematic sampling help. Stratified sampling practice questions corbettmaths. With this quiz and worksheet, youll be asked to differentiate cluster. Stratified random sampling provides the benefit of a more accurate sampling of a population, but can be disadvantageous when researchers. The systematic sample can also be viewed as if arising as a stratified sample. Data collection and sampling introduction to fieldwork. In a systematic sample, measurements are taken at regular. Sep 30, 20 this study attempted to find a stratified sampling design based on data mining methods that achieves improved sampling efficiency over designs conventionally used in studies of healthcare providers for management and policy decisions in south korea. 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. Updated for the 2012 exam ultimate gcse statistics revision guide. 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. I am thinking of using a stratified random sample of my models from the raster package in r. Systematic sampling is similar to arithmetic progression. Each element has an equal probability of selection, but combinations of elements have different probabilities.
In stratified random sampling or stratification, the strata are formed based on members shared attributes or characteristics. Gcse mathematics stratified sampling 3 minute maths. Suppose you want to choose 100 students for a survey. Stratified random sampling the way in which was have selected sample units thus far has required us to know little about the population of interest in advance of selecting the sample. Imagine slips of paper each with a persons name, put all the slips into a barrel, mix them up, then dive your hand in and choose some slips of paper. Whats the difference between stratified and systematic. Stratified sampling meaning in the cambridge english dictionary. Systematic sampling is when a researcher selects every nth person on the sampling frame to be part of the sample. A worksheet and exam style practice questions covering gcse stratified sampling. This is where observations are taken at regular intervals. Stratified random sampling occurs when the population is divided into groups, or strata, according to selected variables e. Sampling mathematics alevel revision revision maths. The main things to remember when working with gcse mathematics stratified sampling questions are. Lesson includes definition and builds the difficulty of examples which my class found insightful.
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