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