Population and sampling in research methodology

Sampling (statistics)

First, identifying strata and implementing such an approach can increase the cost and complexity of sample selection, as well as leading to increased complexity of population estimates. This would be the population being analyzed in the study, but it would be impossible to collect information from all female smokers in the U.

Random sampling — every member has an equal chance Stratified sampling — population divided into subgroups strata and members are randomly selected from each group Systematic sampling — uses a specific system to select members such as every 10th person on an alphabetized list Cluster random sampling — divides the population into clusters, clusters are randomly selected and all members of the cluster selected are sampled Multi-stage random sampling — a combination of one or more of the above methods Non-probability Sampling — Does not rely on the use of randomization techniques to select members.

In some cases, an older measurement of the variable of interest can be used as an auxiliary variable when attempting to produce more current estimates. This is typically done in studies where randomization is not possible in order to obtain a representative sample.

These conditions give rise to exclusion biasplacing limits on how much information a sample can provide about the population. Bias is more of a concern with this type of sampling. True In the real world, the actual situations is that the null hypothesis is: The combination of these traits makes it possible to produce unbiased estimates of population totals, by Population and sampling in research methodology sampled units according to their probability of selection.

A population can be defined as including all people or items with the characteristic one wishes to understand.

General rule - as large as possible to increase the representativeness of the sample Increased size decreases sampling error Relatively small samples in qualitative, exploratory, case studies, experimental and quasi-experimental studies Descriptive studies need large samples; e.

We visit every household in a given street, and interview the first person to answer the door. Systematic sampling A visual representation of selecting a random sample using the systematic sampling technique Systematic sampling also known as interval sampling relies on arranging the study population according to some ordering scheme and then selecting elements at regular intervals through that ordered list.

Under the sampling scheme given above, it is impossible to get a representative sample; either the houses sampled will all be from the odd-numbered, expensive side, or they will all be from the even-numbered, cheap side, unless the researcher has previous knowledge of this bias and avoids it by a using a skip which ensures jumping between the two sides any odd-numbered skip.

For instance, an investigation of supermarket staffing could examine checkout line length at various times, or a study on endangered penguins might aim to understand their usage of various hunting grounds over time. Another drawback of systematic sampling is that even in scenarios where it is more accurate than SRS, its theoretical properties make it difficult to quantify that accuracy.

However, in the more general case this is not usually possible or practical. As long as the starting point is randomizedsystematic sampling is a type of probability sampling.

The group of units or individuals who have a legitimate chance of being selected are sometimes referred to as the sampling frame. Time spent in making the sampled population and population of concern precise is often well spent, because it raises many issues, ambiguities and questions that would otherwise have been overlooked at this stage.

Sampling Methods for Quantitative Research Sampling Methods Sampling and types of sampling methods commonly used in quantitative research are discussed in the following module. These various ways of probability sampling have two things in common: Extra care has to be taken to control biases when determining sampling techniques.

Students in those preschools could then be selected at random through a systematic method to participate in the study. The different types of non-probability sampling are as follows: The results usually must be adjusted to correct for the oversampling.

For example, we can allocate each person a random number, generated from a uniform distribution between 0 and 1, and select the person with the highest number in each household.

There are several variations on this type of sampling and following is a list of ways probability sampling may occur: Often there is large but not complete overlap between these two groups due to frame issues etc.

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Stratified sampling A visual representation of selecting a random sample using the stratified sampling technique When the population embraces a number of distinct categories, the frame can be organized by these categories into separate "strata. If periodicity is present and the period is a multiple or factor of the interval used, the sample is especially likely to be unrepresentative of the overall population, making the scheme less accurate than simple random sampling.

Where voting is not compulsory, there is no way to identify which people will actually vote at a forthcoming election in advance of the election.Gamma g is calculated based on population data from prior research studies, or determined several different ways depending on the nature of the data and the statistical tests to be performed The textbook discusses 4 ways to estimate gamma (population effect size) based upon.

May 26,  · Dr. Manishika Jain in this lecture explains the meaning of Sampling & Types of Sampling Research Methodology Population &.

A research population is generally a large collection of individuals or objects that is the main focus of a scientific query. It is for the benefit of.

Research Population

In non-probability sampling, on the other hand, sampling group members are selected on non-random manner, therefore not each population member has a chance to participate in the study. Non-probability sampling methods include purposive, quota, convenience and snowball sampling methods.

Population and sample. Sampling techniques Let us extend in this chapter what we have already presented in the beginning of Descriptive Statistics, including now the definition of some sampling techniques and concepts in order to be able to decide which is the appropriate sampling technique for each situation.

In statistics, quality assurance, and survey methodology, sampling is the selection of a subset (a statistical sample) of individuals from within a statistical population to estimate characteristics of the whole population.

Two advantages of sampling are that the cost is lower and data collection is faster than measuring the entire population.

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Population and sampling in research methodology
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