Study on a stratified sampling investigation method for. 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. The elements in the population are divided into layersgroups strata based on their values on oneseveral auxiliary variables. Proportionate allocation uses a sampling fraction in each of the strata that is proportional to that of the total population. The strata or subgroups should be different and the data should not overlap.
While using stratified sampling, the researcher should use simple probability sampling. Twophase stratified sampling happens to be a powerful and cost effective economical technique for obtaining the. Sampling and sample size determination stratified sampling. Koether hampdensydney college tue, jan 31, 2012 robb t. In general terms, the estimate for the population mean used in stratified sampling yst. Stratified sampling definition of stratified sampling by. Stratified random sampling intends to guarantee that the sample represents specific subgroups or strata. Article information, pdf download for stratified sampling using. The stratified sampling calculator was developed by jacob cons. We now consider the estimation of population mean and population variance from a stratified sample. 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.
Entire population sampling unit unbiased estimator simple random sample stratify random sample these keywords were added by machine and not by the authors. Unlike the simple random sample and the systematic random sample, sometimes we are interested in particular strata meaning groups within the population e. Proportional stratified sampling pdf stratified sampling offers significant improvement to simple random. Stratified and poststratified sampling schemes are useful survey techniques commonly used by government agencies. And, because variance between stratified sampling variance is lower than that of srs.
Quota sampling is the nonprobability version of stratified sampling. A stratified random sample is one obtained by separating the population elements into nonoverlapping groups, called strata and then selecting a simple random sample from each stratum. Stratified random sampling is a type of probability sampling technique see our article probability sampling if you do not know what probability sampling is. This will enable you to compare your subgroup with the rest of the population with greater accuracy, and at lower cost. Stratified random sampling provides better precision as it takes the samples proportional to the random population. Random sampling chooses a number of subjects from each subset with, unlike a quota sample, each potential subject having a known probability of being. Total sample size k i i nn population n units stratum 1. Across the united states, the practices for collecting water use data. Feb 08, 2012 sampling provides an uptodate treatment of both classical and modern sampling design and estimation methods, along with sampling methods for rare, clustered, and hardtodetect populations. Stratified sample definition and meaning collins english. Number of sampling units to be drawn from ith stratum. This is a website which cointains a stratified sampling calculator to save you time from having to do the maths. 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. The estimate for mean and total are provided when the sampling scheme is stratified 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. In taking a sample of villages from a big state, it is more administratively convenient to consider the districts as strata so that the administrative set up at district level may be used. Scribd is the worlds largest social reading and publishing site. Assuming that the cost of sampling does not vary from category to category. Following considerations should be kept in mind for stratified sampling. The sampling frame is the list of ultimate sampling entities, which may be people, households, organizations, or other units of analysis.
Pdf stratified sampling design based on data mining. A simple random sample is used to represent the entire data population. Scalable simple random sampling and strati ed sampling both kand nare given and hence the sampling probability p kn. The strata must be non overlapping and together constitute the whole population. Thematic guidelines sampling wfp remote access secure services. In case of stratified sampling, variance between 0, i. Stratified sampling is a common sampling technique used by researchers when trying to draw conclusions from different subgroups or strata. The principal reasons for using stratified random sampling rather than simple random sampling are as follows. If you continue browsing the site, you agree to the use of cookies on this website. In stratified sampling, subsets of the population are created so that each subset has a common characteristic, such as gender. Since it is a unit free measure, it is often used to compare the precision levels of. Stratified random sampling to estimate water use estimating. Stratified random sampling ensures that no any section of the population are underrepresented or overrepresented. The stratified random sampling approach allows explicit estimation of the error due to sampling.
In the panel data setting, g is the number of crosssectional units and mg is the number of time periods for unit g. Scalable simple random sampling and strati ed sampling. It is an easy to use stratified sampling calculator which only requires minum data input. After dividing the population into strata, the researcher randomly selects the sample proportionally. An excel sheet and word document explaining stratified sampling. 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 actually not a new sampling design of its own, but a procedural method to subdivide a population into separate and more homogeneous subpopulations called strata kleinn 2007 1.
In stratified random sampling, all the strata of the population is sampled while in cluster sampling, the researcher only randomly selects a number of clusters from the collection of clusters of the entire population. While using stratified sampling, the researcher should use simple probability. Feb 15, 2009 stratified random sampling slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. And, because variance between 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 stratified sample is one that ensures that subgroups strata of a given population are each adequately represented within the whole sample population of a research study. Apr 19, 2019 simple random samples and stratified random samples are both statistical measurement tools. Stratified and poststratified sampling schemes are useful survey techniques commonly used by government agencies, private consultants, and applied statisticians.
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. Stratified random sampling helps minimizing the biasness in selecting the samples. Sampling ppt free download as powerpoint presentation. This work is licensed under a creative commons attribution. The main difference between cluster sampling and stratified sampling lies with the inclusion of the cluster or strata. This third edition retains the general organization of the two previous editions, but incorporates extensive new materialsections, exercises, and. 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. Cochran 1977 provides a modification if sampling costs do depend on category 3. 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. In some situations it is useful from a statistical point of view, or required for practical and organizational reasons, to subdivide the. This is because this type of sampling technique has a high statistical precision compared to simple random sampling. The strata is formed based on some common characteristics in the population data. This approach is ideal only if the characteristic of interest is distributed homogeneously across the population. The results showed that conducting a stratified resident travel investigation in accordance with the characteristics of residential areas will yield samples with much smaller differences and reduce the investigation sampling rate.
Administrative convenience can be exercised in stratified sampling. For example if l is the number of strata or depths and. Stratified sampling a modification of either simple random or system atic sampling is first to divide. Sample size requirements for stratified random sampling of. This process is experimental and the keywords may be updated as the learning algorithm improves. This text first dissected the relationship between average travel frequency, trip mode structure, and the characteristics of residential areas. Understanding stratified samples and how to make them. Samples are selected independently from each stratum. Proportionate stratified sampling in this the number of units selected from each stratum is proportionate to the share of stratum in the population e. Three techniques are typically used in carrying out step 6. 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. Sampling ppt stratified sampling sampling statistics. Stratified sampling for oversampling small subpopulations. In terms of sampling fractions we have,f1 f2 fh f which is the overall sampling fraction.
Sampling theory chapter 4 stratified sampling shalabh, iit kanpur page 2 notations. 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. Sampling theory chapter 4 stratified sampling shalabh, iit kanpur page 7 3. Regional workshop on the use of sampling in agricultural surveys. Development of estimation procedure of population mean in two. 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. In actuality, cochran 1977 developed the result in equation 5. Students learn the difference between different types of sampling methods and how to calculate a stratified sample size using equal proportions. This links with the maths agony aunt article in the tes dated 040305. For example, one might divide a sample of adults into subgroups by age, like 1829, 3039, 4049, 5059, and 60 and above. Sampling and sample size determination free download as powerpoint presentation.
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