### Sampling opportunity -

Convenience sampling is characterized with insufficient power to identify differences of population subgroups. Contents move to sidebar hide.

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Download as PDF Printable version. Sampling from the part of the population close at hand. This section does not cite any sources. Please help improve this section by adding citations to reliable sources.

Unsourced material may be challenged and removed. November Learn how and when to remove this template message. Practical sampling [ Newbury Park: Sage Publications.

ISBN Research in health care : concepts, designs and methods Reprinted. Cheltenham: N. The Sage encyclopedia of qualitative research methods. Los Angeles, Calif. SAGE Publications. doi : Educational research : quantitative, qualitative, and mixed approaches 4th ed.

Thousand Oaks, Calif. This is a quick and easy way to access a sample, so practicality is an advantage. But the resultant sample would not be representative and therefore findings would not be generalisable.

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Shop All Resources Student Resources Assessment Resources Teaching Resources. In this technique, the population is segmented into mutually-exclusive subgroups just as in stratified sampling , and then a non-random set of observations is chosen from each subgroup to meet a predefined quota.

In proportional quota sampling , the proportion of respondents in each subgroup should match that of the population. But you will have to stop asking Hispanic-looking people when you have 15 responses from that subgroup or African-Americans when you have 13 responses even as you continue sampling other ethnic groups, so that the ethnic composition of your sample matches that of the general American population.

In this case, you may decide to have 50 respondents from each of the three ethnic subgroups Caucasians, Hispanic-Americans, and African- Americans , and stop when your quota for each subgroup is reached.

Neither type of quota sampling will be representative of the American population, since depending on whether your study was conducted in a shopping center in New York or Kansas, your results may be entirely different.

The non-proportional technique is even less representative of the population but may be useful in that it allows capturing the opinions of small and underrepresented groups through oversampling. Expert sampling. This is a technique where respondents are chosen in a non-random manner based on their expertise on the phenomenon being studied.

For instance, in order to understand the impacts of a new governmental policy such as the Sarbanes-Oxley Act, you can sample an group of corporate accountants who are familiar with this act.

The advantage of this approach is that since experts tend to be more familiar with the subject matter than non-experts, opinions from a sample of experts are more credible than a sample that includes both experts and non-experts, although the findings are still not generalizable to the overall population at large.

Snowball sampling. In snowball sampling, you start by identifying a few respondents that match the criteria for inclusion in your study, and then ask them to recommend others they know who also meet your selection criteria.

For instance, if you wish to survey computer network administrators and you know of only one or two such people, you can start with them and ask them to recommend others who also do network administration.

Although this method hardly leads to representative samples, it may sometimes be the only way to reach hard-to-reach populations or when no sampling frame is available. In the preceding sections, we introduced terms such as population parameter, sample statistic, and sampling bias.

In this section, we will try to understand what these terms mean and how they are related to each other. In other words, a response is a measurement value provided by a sampled unit. Each respondent will give you different responses to different items in an instrument.

Responses from different respondents to the same item or observation can be graphed into a frequency distribution based on their frequency of occurrences.

For a large number of responses in a sample, this frequency distribution tends to resemble a bell-shaped curve called a normal distribution , which can be used to estimate overall characteristics of the entire sample, such as sample mean average of all observations in a sample or standard deviation variability or spread of observations in a sample.

Populations also have means and standard deviations that could be obtained if we could sample the entire population. Sample statistics may differ from population parameters if the sample is not perfectly representative of the population; the difference between the two is called sampling error.

Theoretically, if we could gradually increase the sample size so that the sample approaches closer and closer to the population, then sampling error will decrease and a sample statistic will increasingly approximate the corresponding population parameter. If a sample is truly representative of the population, then the estimated sample statistics should be identical to corresponding theoretical population parameters.

How do we know if the sample statistics are at least reasonably close to the population parameters? Here, we need to understand the concept of a sampling distribution. Imagine that you took three different random samples from a given population, as shown in Figure 8. If each random sample was truly representative of the population, then your three sample means from the three random samples will be identical and equal to the population parameter , and the variability in sample means will be zero.

But this is extremely unlikely, given that each random sample will likely constitute a different subset of the population, and hence, their means may be slightly different from each other.

However, you can take these three sample means and plot a frequency histogram of sample means. If the number of such samples increases from three to 10 to , the frequency histogram becomes a sampling distribution.

Hence, a sampling distribution is a frequency distribution of a sample statistic like sample mean from a set of samples , while the commonly referenced frequency distribution is the distribution of a response observation from a single sample.

Just like a frequency distribution, the sampling distribution will also tend to have more sample statistics clustered around the mean which presumably is an estimate of a population parameter , with fewer values scattered around the mean. With an infinitely large number of samples, this distribution will approach a normal distribution.

The variability or spread of a sample statistic in a sampling distribution i. In contrast, the term standard deviation is reserved for variability of an observed response from a single sample.

The mean value of a sample statistic in a sampling distribution is presumed to be an estimate of the unknown population parameter. Based on the spread of this sampling distribution i.

Confidence interval is the estimated probability that a population parameter lies within a specific interval of sample statistic values.

All normal distributions tend to follow a percent rule see Figure 8. Since a sampling distribution with an infinite number of samples will approach a normal distribution, the same rule applies, and it can be said that:. Skip to main content. Main Body. Search for:.

The Sampling Process Figure 8.

One Affordable eatery specials the most important issues about any type opportujity method is how ppportunity of samplling population the results are. The population opportunitu the group opportnity people from Budget-friendly food subscription packages the sample is drawn. For sampliny sampling opportunity the ssampling of participants is Free party loot bags from sixth form colleges in Hull, the findings of the oppodtunity can only be applied to that group of people and not all sixth form students in the UK and certainly not all people in the world. Obviously it is not usually possible to test everyone in the target population so therefore psychologists use sampling techniques to choose people who are representative typical of the population as a whole. Opportunity sampling is the sampling technique most used by psychology students. It consists of taking the sample from people who are available at the time the study is carried out and fit the criteria your are looking for. This may simple consist of choosing the first 20 students in your college canteen to fill in your questionnaire. Grade Booster exam Cheap beauty treatments for ssampling Opportunity Budget-friendly food subscription packages is where a researcher samling participants based on Budget-friendly food subscription packages availability. One example would be standing on the street asking passers by to join the research. This is a quick and easy way to access a sample, so practicality is an advantage. But the resultant sample would not be representative and therefore findings would not be generalisable.
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