- Snowball sampling. (surveymonkey.com)
- Snowball sampling is best for surveys targeting specific groups that are hard to find or reach, like undocumented immigrants or people with rare health problems. (surveymonkey.com)
- In sociology and statistics research, snowball sampling (or chain sampling, chain-referral sampling, referral sampling) is a nonprobability sampling technique where existing study subjects recruit future subjects from among their acquaintances. (wikipedia.org)
- Thus the sample group is said to grow like a rolling snowball. (wikipedia.org)
- As sample members are not selected from a sampling frame, snowball samples are subject to numerous biases. (wikipedia.org)
- When virtual social networks are used, then this technique is called virtual snowball sampling. (wikipedia.org)
- It was widely believed that it was impossible to make unbiased estimates from snowball samples, but a variation of snowball sampling called respondent-driven sampling has been shown to allow researchers to make asymptotically unbiased estimates from snowball samples under certain conditions. (wikipedia.org)
- Snowball sampling and respondent-driven sampling also allows researchers to make estimates about the social network connecting the hidden population. (wikipedia.org)
- Snowball sampling uses a small pool of initial informants to nominate, through their social networks, other participants who meet the eligibility criteria and could potentially contribute to a specific study. (wikipedia.org)
- The term "snowball sampling" reflects an analogy to a snowball increasing in size as it rolls downhill Draft a participation program (likely to be subject to change, but indicative). (wikipedia.org)
- Snowball sampling is quite suitable to use when members of a population are hidden and difficult to locate (e.g. samples of the homeless or users of illegal drugs) and these members are closely connected (e.g. organized crime, sharing similar interests, involvement in the same groups that are relevant to the project at hand). (wikipedia.org)
- 1. Social computing Snowball sampling can be perceived as an evaluation sampling in the social computing field. (wikipedia.org)
- For example, in the interview phase, snowball sampling can be used to reach hard-to-reach populations. (wikipedia.org)
- Snowball sampling has demonstrated as a second best method in conducting research in conflict environments like, in the context of the Israel and Arab Conflict. (wikipedia.org)
- Snowball sampling allows the investigators to approach the marginalized population at cognitive and emotional level and enroll them in study. (wikipedia.org)
- Snowball sampling address the conditions of lack of trust that arises due to uncertainty about the future through trace-linking methodology. (wikipedia.org)
- 3. Expert information collection Snowball sampling can be used to identify experts in a certain field such as medicine, manufacturing processes, or customer relation methods, and gather professional and valuable knowledge. (wikipedia.org)
- For instance, 3M called in specialists from all fields that related to how a surgical drape could be applied to the body using snowball sampling. (wikipedia.org)
- Snowball sampling - The first respondent refers an acquaintance. (wikipedia.org)
- Along with convenience sampling and snowball sampling, consecutive sampling is one of the most commonly used kinds of nonprobability sampling. (wikipedia.org)
- Some examples of nonrandom samples are convenience samples, judgment samples, purposive samples, quota samples, snowball samples, and quadrature nodes in quasi-Monte Carlo methods. (wikipedia.org)

- Based on the expressed focus and emphasis of the survey, an evaluation of the distribution of 1992 deaths was undertaken to assist in the identification of sample strata. (cdc.gov)
- This evaluation established four basic criteria for the identification of sampling strata: age, race, gender, and cause of death. (cdc.gov)
- Certificates from the CMS were selected with certainty for 12 of the 50 strata (see table A), representing 45-percent of the total sample of 22,957 certificates. (cdc.gov)
- For the remaining 38 non-certainty strata, the sampling interval or "take every" values ranged from 1.09 to 115.24. (cdc.gov)
- Larger samples are taken in the strata with the greatest variability to generate the least possible overall sampling variance. (wikipedia.org)
- The reasons to use stratified sampling rather than simple random sampling include If measurements within strata have lower standard deviation, stratification gives smaller error in estimation. (wikipedia.org)
- In stratified sampling, the sampling is done on elements within each strata. (wikipedia.org)

- Overall, keeping the sample as complete and representative as possible requires sound judgment and quality training of interview teams. (cdc.gov)
- Judgment sample is a type of nonrandom sample that is selected based on the opinion of an expert. (wikipedia.org)

- Then simple random sampling or systematic sampling is applied within each stratum. (wikipedia.org)
- Then methods such as simple random sampling or systematic sampling can be applied within each stratum. (wikipedia.org)

- Though most random phenomena do not have equally likely outcomes, it can be helpful to define a sample space in such a way that outcomes are at least approximately equally likely, since this condition significantly simplifies the computation of probabilities for events within the sample space. (wikipedia.org)
- If all first-order inclusion probabilities are equal, Poisson sampling becomes equivalent to Bernoulli sampling, which can therefore be considered to be a special case of Poisson sampling. (wikipedia.org)
- Systematic sampling may also be used with non-equal selection probabilities. (wikipedia.org)

- The survey focuses on a nationally representative sample of individuals aged 15 year and over who were residents of the United States and died in 1993. (cdc.gov)
- Increase the precision of your sample or ensure a representative sample from key groups. (ibm.com)
- However, in research, because of time constraint and budget, a representative sample are normally used. (slideshare.net)
- Participants' decision to participate may be correlated with traits that affect the study, making the participants a non-representative sample. (wikipedia.org)
- In 2009, Representative Sample joined a one-third minority in opposing an increase in the state minimum wage. (wikipedia.org)
- An unbiased (representative) sample is a set of objects chosen from a complete sample using a selection process that does not depend on the properties of the objects. (wikipedia.org)
- This kind of sample will also be a wider representative sample. (wikipedia.org)

- Higher sampling error, which can be expressed in the so-called "design effect", the ratio between the number of subjects in the cluster study and the number of subjects in an equally reliable, randomly sampled unclustered study. (wikipedia.org)

- Convenience sampling is a form of non-probability sampling that involves selection based on availability, opportunity, or convenience. (cdc.gov)
- Systematic random sampling involves the selection of every k -th element (or block of elements) from a list of elements, starting with any randomly selected element. (encyclopedia.com)
- In survey sampling it most often involves a questionnaire used to measure the characteristics and/or attitudes of people. (wikipedia.org)
- The technique involves pouring the sample so that it takes on a conical shape, and then flattening it out into a cake. (wikipedia.org)

- Clustered sampling: select clusters-groups of sampling units. (ibm.com)
- Select clusters or groups of sampling units to make surveys more cost effective. (ibm.com)
- A CASPER Toolbox is available for GIS sample selection that can automatically select clusters. (cdc.gov)
- Using all the sample elements in all the selected clusters may be prohibitively expensive or unnecessary. (wikipedia.org)
- A random sampling technique is then used on any relevant clusters to choose which clusters to include in the study. (wikipedia.org)
- When the clusters are of different sizes, probability proportionate to size sampling is used. (wikipedia.org)

- Watch a brief demonstration of IBM SPSS Complex Samples in action. (ibm.com)

- You can reach correct point estimates, predict numerical and categorical outcomes from nonsimple random samples and account for up to three stages when analyzing data from a multistage design. (ibm.com)
- For computer simulation, see pseudo-random number sampling . (wikipedia.org)
- Random sampling (and sampling error) can only be used to gather information about a single defined point in time. (wikipedia.org)
- In probability theory , the sample space (also called sample description space or possibility space ) of an experiment or random trial is the set of all possible outcomes or results of that experiment. (wikipedia.org)
- This may seem like a random probability sampling design, but consider this: there's probably a difference between the type of people who can come to your store in the morning versus those who have to visit later. (surveymonkey.com)
- To select the seven households to interview, conduct systematic random sampling . (cdc.gov)
- This led to speculation that more than simple random sampling error was involved. (encyclopedia.com)
- Eleven random samples which, when combined, included roughly 20,000 questions-questions we can confidently say are representative of (or look a lot like) the entire pool of SurveyMonkey customer questions on the same 11 topics. (surveymonkey.com)
- Instead if we choose to take a random sample of 10, 20 and 30 from Town A, B and C respectively then we can produce a smaller error in estimation for the same total size of sample. (wikipedia.org)
- Probability sampling, or random sampling, is a sampling technique in which the probability of getting any particular sample may be calculated. (wikipedia.org)
- In quota sampling, there is non-random sample selection and this can be unreliable. (wikipedia.org)
- This non-random element is a source of uncertainty about the nature of the actual sample and quota versus probability has been a matter of controversy for many years. (wikipedia.org)
- Rejection sampling is based on the observation that to sample a random variable one can perform a uniformly random sampling of the 2D cartesian graph, and keep the samples in the region under the graph of its density function. (wikipedia.org)
- To visualize the motivation behind rejection sampling, imagine graphing the density function of a random variable onto a large rectangular board and throwing darts at it. (wikipedia.org)
- Suppose you want to sample some random variable X with distribution f(x). (wikipedia.org)
- The best way to avoid a biased or unrepresentative sample is to select a random sample, also known as a probability sample. (wikipedia.org)
- A sample that is not random is called a non-random sample or a non-probability sampling. (wikipedia.org)
- is a set of n independent, identically distributed (iid) random variables with distribution F. A sample concretely represents n experiments in which the same quantity is measured. (wikipedia.org)
- Note that a sample of random variables (i.e. a set of measurable functions) must not be confused with the realizations of these variables (which are the values that these random variables take, formally called random variates). (wikipedia.org)
- For problems in which the dependence of the performance function is only moderately non-linear with respect to the parameters modeled as random variables, setting the importance direction as the gradient vector of the performance function in the underlying standard normal space leads to highly efficient Line Sampling. (wikipedia.org)
- The idea behind importance sampling is that certain values of the input random variables in a simulation have more impact on the parameter being estimated than others. (wikipedia.org)
- This makes systematic sampling functionally similar to simple random sampling (SRS). (wikipedia.org)
- This is random sampling with a system. (wikipedia.org)
- From the sampling frame, a starting point is chosen at random, and choices thereafter are at regular intervals. (wikipedia.org)
- Another advantage is that random samples can be taken one at a time, remembering which samples were taken so far. (wikipedia.org)
- In two dimensions the difference between random sampling, Latin Hypercube sampling and orthogonal sampling can be explained as follows: In random sampling new sample points are generated without taking into account the previously generated sample points. (wikipedia.org)
- Thus, orthogonal sampling ensures that the ensemble of random numbers is a very good representative of the real variability, LHS ensures that the ensemble of random numbers is representative of the real variability whereas traditional random sampling (sometimes called brute force) is just an ensemble of random numbers without any guarantees. (wikipedia.org)
- A simple random sample is an unbiased surveying technique. (wikipedia.org)
- The principle of simple random sampling is that every object has the same probability of being chosen. (wikipedia.org)
- Although simple random sampling can be conducted with replacement instead, this is less common and would normally be described more fully as simple random sampling with replacement. (wikipedia.org)
- Conceptually, simple random sampling is the simplest of the probability sampling techniques. (wikipedia.org)
- Several efficient algorithms for simple random sampling have been developed. (wikipedia.org)
- Random sampling can also be accelerated by sampling from the distribution of gaps between samples, and skipping over the gaps. (wikipedia.org)

- Good sub-sampling technique becomes important when the large sample is not homogeneous. (wikipedia.org)

- Supported by the Rainbow Warrior, Greenpeace experts conduct independent radiation sampling along the Fukushima coastline. (greenpeace.org)
- University of Minnesota researchers are looking for sites to conduct additional sampling! (google.com)

- James Sample was married to Ernestine F. Sample (August 15, 1909 - September 6, 1980). (wikipedia.org)
- Sample made his debut for Cumberland in the 1980 Minor Counties Championship against Lincolnshire. (wikipedia.org)
- Sample played Minor counties cricket for Cumberland from 1980 to 1992, including 31 Minor Counties Championship matches and 4 MCCA Knockout Trophy matches. (wikipedia.org)

- The over-sampled subgroups include black decedents, female decedents, decedents under age 35, and decedents over age 99. (cdc.gov)

- An estimate of a quantity of interest, such as an average or percentage, will generally be subject to sample-to-sample variation. (wikipedia.org)

- Quota sampling. (surveymonkey.com)
- Quota sampling ensures that you get at least some respondents from all the subpopulations you're interested in, even though this still isn't a true probability sample. (surveymonkey.com)
- Quota sampling is useful when time is limited, a sampling frame is not available, the research budget is very tight or when detailed accuracy is not important. (wikipedia.org)
- Quota sampling is the non probability version of stratified sampling. (wikipedia.org)

- If you were to uniformly sample X, each value would have the same likelihood of being sampled, and your distribution would be of the form f(x)=y for some y value instead of some non-uniform function f(x). (wikipedia.org)

- As with the Nyquist-Shannon sampling theorem, this theorem also assumes an idealization of any real-world situation, as it only applies to functions that are sampled over an infinitude of points. (wikipedia.org)
- Nonuniform sampling is a branch of sampling theory involving results related to the Nyquist-Shannon sampling theorem. (wikipedia.org)
- Nonuniform sampling is based on Lagrange interpolation and the relationship between itself and the (uniform) sampling theorem. (wikipedia.org)
- Nonuniform sampling is a generalisation of the Whittaker-Shannon-Kotelnikov (WSK) sampling theorem. (wikipedia.org)
- The above is called the Paley-Wiener-Levinson theorem, which generalize WSK sampling theorem from uniform samples to non uniform samples. (wikipedia.org)

- Risk of incorrect rejection: the risk that the sample supports the conclusion that the recorded amount balance is materially misstated when it is not materially misstated. (wikipedia.org)
- Rejection sampling works as follows: Sample a point on the x-axis from the proposal distribution. (wikipedia.org)

- This PowerPoint provides an overview of types of samples, explains when each is appropriate, and discusses how to determine sample size. (ncsl.org)
- What is sample size? (slideshare.net)
- Understand the significance of sample size. (slideshare.net)
- 5. Availability of resources sets the upper limit of the sample size. (slideshare.net)
- Optimum sample size determination is required for the following reasons: 4. (slideshare.net)
- 9. CONVERSELY If the sample size is too large: 2. (slideshare.net)
- Auditors can lower the sampling risk by increasing the sampling size. (wikipedia.org)
- Note that the samples do not have to be equal size and not all samples are mandatory in a pixel. (wikipedia.org)
- An important implication of this formula is that the sample size must be quadrupled (multiplied by 4) to achieve half (1/2) the measurement error. (wikipedia.org)
- When choosing a Sampling Valve, different factors have to be considered: The material, pressure and temperature rating, gaskets, size and position of the valve according to the pipe specification of the plant. (wikipedia.org)
- 3. Changing the size of your sample during the course of the research The first two features of a theoretical sample deals with issues right at the beginning of the research project. (wikipedia.org)
- This must be translated into an assessment both of sample portion size and number, and the frequency of taking samples. (wikipedia.org)
- Much of the legislation relates to food as supplied to a consumer, meaning that every portion of a size of perishable food and foods at risk as may be supplied to a consumer has to comply, so that in such cases the sample submitted for analysis could simply be an entire consumer-sized portion. (wikipedia.org)
- There are exceptions, however, such as the sampling of nut products for the presence of aflatoxins, which stipulate a primary sample size related to the size of the consignment - with associated requirements for initial homogenisation to produce a smaller sample to be sent for analysis. (wikipedia.org)
- Larger sample size will reduce the chance of sampling error occurring. (wikipedia.org)
- Even if a material sample is not countable as individual items, the quantity of the sample may still be describable in terms of its volume, mass, size, or other such dimensions. (wikipedia.org)
- However it is not the same as SRS because not every possible sample of a certain size has an equal chance of being chosen (e.g. samples with at least two elements adjacent to each other will never be chosen by systematic sampling). (wikipedia.org)
- It is usually necessary to increase the total sample size to achieve equivalent precision in the estimators, but cost savings may make such an increase in sample size feasible. (wikipedia.org)
- We continue until we have sample of desired size k. (wikipedia.org)

- To illustrate the danger of systematic skip concealing a pattern, suppose we were to sample a planned neighborhood where each street has ten houses on each block. (wikipedia.org)

- Similarly, the configuration of uniformly spaced sampling points in one-dimension can be generalized to a lattice in higher dimensions. (wikipedia.org)
- Therefore, although uniformly spaced samples may result in easier reconstruction algorithms, it is not a necessary condition for perfect reconstruction. (wikipedia.org)

- A more complete description of outcomes, however, could specify both the denomination and the suit, and a sample space describing each individual card can be constructed as the Cartesian product of the two sample spaces noted above (this space would contain fifty-two equally likely outcomes). (wikipedia.org)
- Flipping a coin leads to a sample space composed of two outcomes that are almost equally likely. (wikipedia.org)
- The sampling theory of Shannon can be generalized for the case of nonuniform samples, that is, samples not taken equally spaced in time. (wikipedia.org)
- the 36 ordered pairs (D1 , D2) constitute a sample space of equally likely events. (wikipedia.org)
- The sample is dropped into the top, and the box produces two equally divided subsamples. (wikipedia.org)
- In Orthogonal sampling, the sample space is divided into equally probable subspaces. (wikipedia.org)

- Moreover, the in-depth analysis of a small-N purposive sample or a case study enables the "discovery" and identification of patterns and causal mechanisms that do not draw time and context-free assumptions. (wikipedia.org)
- The term sample library, when used in a commercial context, implies a collections of samples that have been produced and licensed for the purpose of being used as samples. (wikipedia.org)
- This selection issue is akin to the truncated regression model where we face selection on the basis of a binary response variable, but the problem has been referred to as length-biased sampling in this specific context. (wikipedia.org)

- René Baños Jorge Chaviano Oscar Porro Abel Sanabria Reinaldo Sanler Renato Mora Una Forma Mas (April 1995) De Vacaciones (July 1997) Live in Berlin (1998) Cambio de Tiempo (April 2002) Akapelleando (January 2008) Vocal Sampling at - retrieved 26 October 2013 - retrieved 26 October 2013 CD liner notes: "Recorded 200% live on August 8th 1997 at the Heimatlklange Festival in Berlin, Germany. (wikipedia.org)
- James W. Sample (October 8, 1910 - October 7, 1995) was an American conductor. (wikipedia.org)
- James Sample died in 1995 of a heart condition in Meadville, Pennsylvania it would have been Samples 85th birthday the day after. (wikipedia.org)

- Although there are many ways of obtaining a discrete representation of a continuous time signal, periodic sampling is by far the simplest scheme. (wikipedia.org)
- Slice sampling, in its simplest form, samples uniformly from underneath the curve f(x) without the need to reject any points, as follows: Choose a starting value x0 for which f(x0)>0. (wikipedia.org)

- The minimum number of samples per unit area required to completely recover the continuous time signal is termed as optimal sampling density. (wikipedia.org)
- Sample uniformly along this line from 0 to the maximum of the probability density function. (wikipedia.org)
- F. Marvasti), Kluwer Academic/Plenum Publishers, New York, 2000 H. J. Landau, "Necessary density conditions for sampling and interpolation of certain entire functions," Acta Math. (wikipedia.org)
- All sample points are then chosen simultaneously making sure that the total ensemble of sample points is a Latin Hypercube sample and that each subspace is sampled with the same density. (wikipedia.org)

- NIOSH considers that all particles entering the sampler should be included as part of the sample whether they deposit on the filter or on the inside surfaces of the sampler. (cdc.gov)
- Numerous research studies have shown that material deposited on the inside surfaces of air sampling cassettes may constitute a significant fraction of the aerosol that enters the sampler. (cdc.gov)
- Consideration of internal sampler wall deposits is included in related international voluntary consensus standards that describe the sampling and analysis of airborne metals and metalloids. (cdc.gov)
- 8 and (4) the use of internal sampling cartridges (sampler inserts). (cdc.gov)

- Optimum allocation (or disproportionate allocation) - The sampling fraction of each stratum is proportionate to both the proportion (as above) and the standard deviation of the distribution of the variable. (wikipedia.org)