Samples are collected and statistics are calculated from the samples so that one can make inferences or extrapolations from the sample to the population. This process of collecting information from a sample is referred to as sampling. Samples : Online and phone-in polls produce biased samples because the respondents are self-selected. In self-selection bias, those individuals who are highly motivated to respond— typically individuals who have strong opinions— are over-represented, and individuals who are indifferent or apathetic are less likely to respond.
A complete sample is a set of objects from a parent population that includes all such objects that satisfy a set of well-defined selection criteria. For example, a complete sample of Australian men taller than 2 meters would consist of a list of every Australian male taller than 2 meters. To compile such a complete sample requires a complete list of the parent population, including data on height, gender, and nationality for each member of that parent population.
In the case of human populations, such a complete list is unlikely to exist, but such complete samples are often available in other disciplines, such as complete magnitude-limited samples of astronomical objects. 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.
However, one chosen from the electoral register might not be unbiased since, for example, males aged under 18 will not be on the electoral register. In an astronomical context, an unbiased sample might consist of that fraction of a complete sample for which data are available, provided the data availability is not biased by individual source properties.
The best way to avoid a biased or unrepresentative sample is to select a random sample, also known as a probability sample. A random sample is defined as a sample wherein each individual member of the population has a known, non-zero chance of being selected as part of the sample. Several types of random samples are simple random samples, systematic samples, stratified random samples, and cluster random samples. A sample that is not random is called a non-random sample, or a non-probability sampling.
Some examples of nonrandom samples are convenience samples, judgment samples, and quota samples. A random sample, also called a probability sample, is taken when each individual has an equal probability of being chosen for the sample. Categorize a random sample as a simple random sample, a stratified random sample, a cluster sample, or a systematic sample.
There is a variety of ways in which one could choose a sample from a population. A simple random sample SRS is one of the most typical ways. Also commonly referred to as a probability sample, a simple random sample of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance of being in the selected sample. An example of an SRS would be drawing names from a hat.
An online poll in which a person is asked to given their opinion about something is not random because only those people with strong opinions, either positive or negative, are likely to respond. Online Opinion Polls : Online and phone-in polls also produce biased samples because the respondents are self-selected. Simple random samples are not perfect and should not always be used. For instance, a simple random sample of ten people from a given country will on average produce five men and five women, but any given trial is likely to over-represent one sex and under-represent the other.
Systematic and stratified techniques, discussed below, attempt to overcome this problem by using information about the population to choose a more representative sample. In addition, SRS may also be cumbersome and tedious when sampling from an unusually large target population. In some cases, investigators are interested in research questions specific to subgroups of the population. For example, researchers might be interested in examining whether cognitive ability as a predictor of job performance is equally applicable across racial groups.
SRS cannot accommodate the needs of researchers in this situation because it does not provide sub-samples of the population. Stratified sampling, which is discussed below, addresses this weakness of SRS. When a population embraces a number of distinct categories, it can be beneficial to divide the population in sub-populations called strata. A population is any complete group with at least one characteristic in common.
Populations are not just people. Populations may consist of, but are not limited to, people, animals, businesses, buildings, motor vehicles, farms, objects or events. These choices will be signaled globally to our partners and will not affect browsing data. We and our partners process data to: Actively scan device characteristics for identification.
I Accept Show Purposes. Your Money. Personal Finance. Your Practice. Popular Courses. Fundamental Analysis Tools for Fundamental Analysis. Table of Contents Expand. What Is Population? Understanding Population. How to Calculate a Population. Population Samples. Real-World Examples of Population. Population FAQs. The Bottom Line. Key Takeaways In ordinary usage, a population is a distinct group of individuals with shared citizenship, identity, or characteristic.
In statistics, a population is a representative sample of a larger group of people or even things with one or more characteristics in common. The members of a sample population must be randomly selected for the results of the study to accurately reflect the whole.
The U. Census is perhaps the most ambitious survey in existence, given that it entails a door-to-door canvas of the entire population rather than a sample group study. Population surveys large and small inform many if not most decisions by government and business. Article Sources. Investopedia requires writers to use primary sources to support their work. These include white papers, government data, original reporting, and interviews with industry experts.
We also reference original research from other reputable publishers where appropriate. You can learn more about the standards we follow in producing accurate, unbiased content in our editorial policy. Compare Accounts. The offers that appear in this table are from partnerships from which Investopedia receives compensation. This compensation may impact how and where listings appear.
Investopedia does not include all offers available in the marketplace. There are various selection methods you can use to select a sample. In small populations, for example the students at a high school, one could conduct a full population survey. In this case, one would speak of a census. This rule applies for all populations: there must be a clear set of rules about who belongs to the group.
0コメント