Stratified Sampling. The selection of one member of the stratum cannot influence the selection of another member. For example, if 65% of population is female, the sample should have 65% of women. 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. The advantages of stratified random samples include increased precision and lower costs. which might have an effect on the research. This often achieves a large sample size through reaching a wide audience, for example with online advertisements. A researcher randomly selects and interviews fifty male and fifty female teachers. 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Random samples are then selected from each stratum. What type of sampling is this? In a proportional stratified sample, the size of each stratum in the sample is proportionate to the size of the stratum in the population. West Yorkshire, It can produce a weighted mean that has less variability than the arithmetic mean of a simple random sample of the population. 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Involves recruiting a sample that is a mini version of the target population; therefore, the researchers recruit participants from each major stratum of the population. The stratified random sample is more representative of the actual population than a random sample because it follows the same proportions of the population. and we are asked to take a sample of 40 staff, stratified according to the above categories. i. systematic ii. random iv. They decide to check on the extent of the problem by having a random sample of the employees und, A medical inspector wants to estimate the overall average monthly occupancy rates of the cancer wards in 80 different hospitals that are evenly located in the northwestern, southeastern, central, and, The executive board of a relatively small university located in Europe wants to determine the attitude of their students toward various aspects of the university. Random samples can be taken from each stratum, or group. Get access risk-free for 30 days, Stratified Sampling. The strengths and weaknesses of these four techniques are summarised below: There are reasons why researchers might choose some sampling techniques rather than others: Most psychologists are lecturers and professors at universities and they have an unfortunate tendency to use the student body as their target population and their own students as the sample. Then random sampling is applied within each stratum. Those who respond to the call for volunteers may all display similar characteristics (such as being more trusting or cooperative than those who did not apply) thus increasing the chances of yielding an unrepresentative sample. Create an account to start this course today. Solve the absolute-value inequality, A study conducted by researchers from the Department of Education wanted to know the average debt of college students in the United States. A systematic method is chosen for selecting from a target group, e.g. Decision theory. convenience iii. For example if every fourth person in the list was male, you would have only males in your sample. Quiz & Worksheet - Elements of a Play or Film Script, Quiz & Worksheet - Persuasive Letter Planning & Layout, Scanning Electron Microscope: Definition & Uses, Demographics for English Language Learners, Tech and Engineering - Questions & Answers, Health and Medicine - Questions & Answers, An upper-level sociology class at a large urban university has 120 students, including 34 seniors, 57 juniors, 22 sophomores, and 7 freshmen. Accordingly, application of stratified sampling method involves dividing population into … A stratified random sample is a random sample in which members of the population are first divided into strata, then are randomly selected to be a part of the sample. Earn Transferable Credit & Get your Degree, Stratified Random Samples: Definition, Characteristics & Examples, Simple Random Samples: Definition & Examples, Cluster Random Samples: Definition, Selection & Examples, Quota Sampling: Definition, Method & Examples, Systematic Random Samples: Definition, Formula & Advantages, Probability Sampling Methods: Multistage, Multiphase, and Cluster Samples, Sampling Techniques In Scientific Investigations, Defining the Difference between Parameters & Statistics, Non-Probability Sampling Methods: Definition & Types, What is Random Sampling? You can test out of the When you are finished, you should be able to: To unlock this lesson you must be a Study.com Member. Stratified sampling is not useful when the population cannot be exhaustively partitioned into disjoint subgroups. It can be difficult and time-consuming to select relevant strata groups for your research study. employees from a conveniently located employer near the laboratory could be selected for the sample group. In general the size of the sample in each stratum is taken in proportion to the size of the stratum. The demographics are as follows: 51% of American college graduates are Caucasian, 22% are African-American, 9% are Asian, 8% are Native American, 5% are Hispanic, 3% are Pacific Islander, and 2% are multiracial. So, we would need (5000 x 0.51) = 2550 Caucasians, (5000 x 0.22) = 1100 African-Americans, (5000 x 0.09) = 450 Asians, (5000 x 0.08) = 400 Native Americans, (5000 x 0.05) = 250 Hispanics, (5000 x 0.03) = 150 Pacific Islanders, and (5000 x 0.02) = 100 multiracial.

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