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Topic: Random sampling

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  Sampling (statistics) - Wikipedia, the free encyclopedia
Sampling is that part of statistical practice concerned with the selection of individual observations intended to yield some knowledge about a population of concern, especially for the purposes of statistical inference.
The sampling frame must be representative of the population and this is a question outside the scope of statistical theory demanding the judgement of experts in the particular subject matter being studied.
However, the importance of random sampling was not universally appreciated and in the USA the 1936 Literary Digest prediction of a Republican win in the presidential election went badly awry, due to severe bias.
en.wikipedia.org /wiki/Sampling_(statistics)   (2031 words)

 PA 765: Sampling
Non-random sampling is widely used as a case selection method in qualitative research, or for quantitative studies of a preliminary and exploratory nature where random sampling is too costly, or where it is the only feasible alternative.
Repeated systematic sample has the side benefit that the variability in the subsample means for a given variable is a measure of the variance of that estimate in the entire sample.
Technically, cluster sampling is where all subjects at the lowest hierarchical level (ex., all students in a school) are sampled for each primary sampling unit (PSU's, which are the second-lowest hierarchical level, such as schools or Census blocks), whereas multistage sampling is where only a random sample of lowest hierarchical level subjects are selected.
www2.chass.ncsu.edu /garson/pa765/sampling.htm   (4807 words)

 Statistics Glossary - sampling
Random sampling is a sampling technique where we select a group of subjects (a sample) for study from a larger group (a population).
Simple random sampling is the basic sampling technique where we select a group of subjects (a sample) for study from a larger group (a population).
Sampling variability refers to the different values which a given function of the data takes when it is computed for two or more samples drawn from the same population.
www.stats.gla.ac.uk /steps/glossary/sampling.html   (1219 words)

 RANDOM SAMPLING   (Site not responding. Last check: 2007-11-07)
For a sample of patients selected from your total patient population, such things as the average age for those people in the sample, the average length of stay as an inpatient, etc., all would be considered statistics.
The advantage of a systematic random sample would be great where my patients are stored in a computer data base and I wish to write a computer program to extract a list for my sample by moving sequentially through the data base.
Then the sample percent equals the strata percent and the sample mean is an estimate of the population mean.
www.hds-healthdatasystems.com /Random.htm   (763 words)

 Survey Sampling Methods
Sampling error is the degree to which a sample might differ from the population.
Stratified sampling is often used when one or more of the stratums in the population have a low incidence relative to the other stratums.
Quota sampling is the nonprobability equivalent of stratified sampling.
www.statpac.com /surveys/sampling.htm   (742 words)

 Sampling   (Site not responding. Last check: 2007-11-07)
In a multistage random sample, a large area, such as a country, is first divided into smaller regions (such as states), and a random sample of these regions is collected.
In the second stage, a random sample of smaller areas (such as counties) is taken from within each of the regions chosen in the first stage.
Then, in the third stage, a random sample of even smaller areas (such as neighborhoods) is taken from within each of the areas chosen in the second stage.
www.stat.yale.edu /Courses/1997-98/101/sample.htm   (589 words)

 Web Site for Perfectly Random Sampling with Markov Chains:
Another problem is that of generating a random spanning tree of a graph or spanning arborescence of a directed graph in accordance with the uniform distribution, or more generally in accordance with a distribution given by weights on the edges of the graph or digraph.
However, the running time of their algorithm is an unbounded random variable whose order of magnitude is typically unknown a priori and which is not independent of the state sampled, so a naive user with limited patience who aborts a long run of the algorithm will introduce bias.
In perfect sampling algorithms, a sample is drawn exactly from the stationary distribution of a chain, as opposed to methods that run the chain ``for a long time'' and create samples drawn from a distribution that is close to the stationary distribution.
dimacs.rutgers.edu /~dbwilson/exact   (14686 words)

 Random Sampling   (Site not responding. Last check: 2007-11-07)
In a random or probability sample, each member of the population has an equal chance of being chosen for the sample, and the sample should accurately represent any characteristics of the population such as ethnicity or gender.
Simple random sampling means identifying each member of the population and then choosing members completely at random.
If there were substantially more of one gender than the other, she might want to choose a proportionally stratified random sample to make sure the sample contained the same gender proportion as the original population.
www.arches.uga.edu /~skwmitch/random.html   (344 words)

 Random sampling
Technique that insures each item in a sample for inspection is selected completely by chance to be measured.
Sampling is more accurate in statistical process control for several reasons including it is less susceptible for 'inspection fatigue' in a process, because there is a lesser chance for errors.
The 10 million samples taken during the depression years were not accurate because in 1936 the people who could afford a phone and magazine subscription did not constitute a random sample.
www.sixsigmaspc.com /dictionary/random-sampling.html   (246 words)

 Probability Sampling   (Site not responding. Last check: 2007-11-07)
Because simple random sampling is a fair way to select a sample, it is reasonable to generalize the results from the sample back to the population.
Simple random sampling is not the most statistically efficient method of sampling and you may, just because of the luck of the draw, not get good representation of subgroups in a population.
The problem with random sampling methods when we have to sample a population that's disbursed across a wide geographic region is that you will have to cover a lot of ground geographically in order to get to each of the units you sampled.
www.socialresearchmethods.net /kb/sampprob.htm   (2446 words)

 Random sampling   (Site not responding. Last check: 2007-11-07)
In random sampling, each item or element of the population has an equal chance of being chosen at each draw.
A sample is random if the method for obtaining the sample meets the criterion of randomness (each element having an equal chance at each draw).
The actual composition of the sample itself does not determine whether or not it was a random sample.
davidmlane.com /hyperstat/A35563.html   (63 words)

 Random Sample (from Internet Glossary of Statistical Terms)
In statistical terms a random sample is a set of items that have been drawn from a population in such a way that each time an item was selected, every item in the population had an equal opportunity to appear in the sample.
It is also important to recognize that when sampling with replacement, it is possible for the same item to appear more than once in a sample and it is possible to draw a random sample that is larger than the population from which it came.
The key idea here is that we either sample with replacement or we draw our samples from a population that is so large that the withdrawal of successive items changes probability by an amount that is too small to be of concern.
www.animatedsoftware.com /statglos/sgrandsa.htm   (448 words)

 On Near-Uniform URL Sampling
The random walks are used to generate random URLs according to a distribution that is nearly equal to the PageRank distribution.
One goal of a random sampling approach is variability; that is, one should be able to repeat the sampling procedure and obtain different random samples for different experiments.
Although the distributions for the samples differ somewhat from that of the original graph, the differences are minor, and are due to the variation inherent in any probabilistic experiment.
www9.org /w9cdrom/88/88.html   (7357 words)

 Stratified Random Sampling   (Site not responding. Last check: 2007-11-07)
In stratified sampling the population of N units is first divided into non-overlapping subpopulations called strata.
If sampling from the strata is simple random sampling then whole procedure is called stratified random sampling.
Sampling problems may differ markedly within a population (eg people in prisons and people outside).
www.csm.uwe.ac.uk /~pwhite/SURVEY1/node29.html   (113 words)

 Simple Random Sampling   (Site not responding. Last check: 2007-11-07)
A sampling procedure that assures that each element in the population has an equal chance of being selected is referred to as simple random sampling.
Some problems that arise from random sampling can be overcome by weighting the sample to reflect the population or universe.
For instance, if in our sample of 100 students we ended up with 60% boys and 40% girls, we could decrease the importance of the characteristics for boys and increase those of the girls to reflect our universe, which is 50/50.
www.ryerson.ca /~mjoppe/ResearchProcess/SimpleRandomSampling.htm   (435 words)

 Random Sampling
One way to estimate the size of a population is to collect data by taking random samples.
Gathering data from a randomly selected sample of a larger area is called sampling.
In a forest that measures 5 miles by 5 miles, a sample was taken to count the number of silver maple trees in the forest.
www.biologycorner.com /worksheets/randomsampling.htm   (466 words)

 Random Selection Software and Random Sampling by RandomBots.com
Random sample from non-numeric data and numeric (multiple ranges) and random date scheduling.
Control random sample distribution to multiple conditions for research projects.
Vortex is a random number generator for integers and floating point numerics.
www.randombots.com   (489 words)

 SAMP: Stratified Random Sampling   (Site not responding. Last check: 2007-11-07)
With stratified random sampling, the population is first divided into a number of parts or 'strata' according to some characteristic, chosen to be related to the major variables being studied.
Simple random samples are then selected from each stratum.
The same proportion will be selected within each stratum, making the sample a proportionately stratified random sample.
www.soc.surrey.ac.uk /samp/strat.php   (141 words)

 Simple Random Sampling
The study population is a junior high school with a total of 4,000 students in grades 7, 8, and 9.
Selection by simple random sampling means that all students have an equal chance or being selected, and no student can be selected more than once.
Each student selected for the sample was asked how much he spends for ice cream per week, on the average.
www.dnr.state.ak.us /ssd/whtest/sashtml/stat/chap61/sect3.htm   (540 words)

 Research Randomizer: Instant Random Sampling and Random Assignment
This web site is designed to assist researchers and students who want an easy way to perform random sampling or assign participants to experimental conditions.
Research Randomizer can be used in a wide variety of situations, including psychological experimentation, medical trials, and survey research.
See some examples of how Research Randomizer can be used for random sampling and random assignment.
www.randomizer.org   (182 words)

 Simple Random Sampling
With simple random sampling and no stratification in the sample design, the selection probability is the same for all units in the sample.
In this sample, the selection probability for each customer equals 0.007423, which is the sample size (100) divided by the population size (13,471).
The sampling weight equals 134.71 for each customer in the sample, where the weight is the inverse of the selection probability.
v8doc.sas.com /sashtml/stat/chap63/sect3.htm   (421 words)

 Random number generator, random name generator, random sampling, random selection software   (Site not responding. Last check: 2007-11-07)
Random number generator, random name generator, random sampling, random selection software
Random sampling from list items which can be loaded from TXT file or added manually one by one.
This randomizer can be used in a wide variety of situations, including psychological experimentation, medical trials, games such as dice game, poker game, free online casino game, etc., generation of cryptographic keys, some classes of scientific experiments and survey research.
supercoolbookmark.com /random   (258 words)

 Simple Random Sampling
In order to answer this question, you draw a sample using simple random sampling from the student population in the junior high school.
You randomly select 40 students and ask them their average weekly expenditure for ice cream, their household income, and the number of children in their household.
The TOTAL=4000 option specifies the total in the population from which the sample is drawn.
support.sas.com /91doc/getDoc/statug.hlp/surveyreg_sect3.htm   (420 words)

 Random Sampling from Databases - Olken (ResearchIndex)   (Site not responding. Last check: 2007-11-07)
Abstract: Random Sampling from Databases by Frank Olken Doctor of Philosophy in Computer Science University of California at Berkeley Professor Michael Stonebraker, Chair In this thesis I describe efficient methods of answering random sampling queries of relational databases, i.e., retrieving random samples of the results of relational queries.
11 Sampling from Spatial Databases (context) - Olken, Rotem - 1993
2 Audit sampling : an introduction to statistical sampling in..
citeseer.ist.psu.edu /5994.html   (2129 words)

 Statistics Glossary - Sampling
b) Those samples in which the same attribute, or variable, is measured twice on each subject, under different circumstances.
Every possible sample of a given size has the same chance of selection; that is, each member of the population is equally likely to be chosen at any stage in the sampling process.
Some reasons for using stratified sampling over simple random sampling are :
www.cas.lancs.ac.uk /glossary_v1.1/samp.html   (1270 words)

 Random Sampling
Random Sampling by Deepak on Tuesday, 7th December 2004
Re: Random Sampling by Tim F on Tuesday, 7th December 2004
Re: Random Sampling by Jeff O on Monday, 13th December 2004
www.isixsigma.com /forum/showmessage.asp?messageID=60507   (327 words)

 Simple Random Sampling   (Site not responding. Last check: 2007-11-07)
The method of simple random sampling (METHOD=SRS) selects units with equal probability and without replacement.
Each possible sample of n different units out of N has the same probability of being selected.
For additional information on simple random sampling algorithms, refer to McLeod and Bellhouse (1983) and Fann, Muller, and Rezucha (1962).
v8doc.sas.com /sashtml/stat/chap63/sect16.htm   (131 words)

 Technorati Tag: random sampling   (Site not responding. Last check: 2007-11-07)
Random Activity Sampling Random and fixed interval activity sampling.
SPN Event Sampling and Marketing Specialized Promotions Network is a California-based national event sampling corporation founded in 1982.
Posts tagged Random Sampling per day for the last 30 days.
www.technorati.com /tag/random+sampling   (276 words)

 Research Randomizer Form
Note: Research Randomizer may not work with AOL browsers or Netscape 6.x.
Also, you may need to disable any pop-up ad blockers you are running because your random numbers will be displayed in a pop-up window (just configure your pop-up blocker to exclude this site.)
To generate a set of random numbers, simply fill out the form, indicating:
www.randomizer.org /form.htm   (420 words)

 Random Sampling Applet   (Site not responding. Last check: 2007-11-07)
It is cited in the truly excellent textbook Exploring Research, Fifth Edition by Neil J. Salkind.
Choose a range for your data, enter how many random numbers you want in your sample, and opt for repetition and ordering.
Oh - one more thing - I am curious as to how this applet is being used.
www.dougshaw.com /sampling   (101 words)

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