Systematic Sampling

(noun)

Systematic sampling relies on arranging the target population according to some ordering scheme, a random start, and then selecting elements at regular intervals through that ordered list.

Related Terms

Examples of Systematic Sampling in the following topics:

  • Sampling Techniques

    • Systematic sampling relies on arranging the target population according to some ordering scheme, a random start, and then selecting elements at regular intervals through that ordered list.
    • As long as the starting point is randomized, systematic sampling is a type of probability sampling.
    • 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.
    • As described above, systematic sampling is an EPS method, because all elements have the same probability of selection.
    • In quota sampling the selection of the sample is non-random.

  • Defining Public Opinion

    • Public opinion can be accurately obtained through a random sample survey, if done correctly.
    • The US Department of Agriculture was one of the first government agencies to sponsor systematic and large scale surveys.

  • Towards a Systematic Conceptualization of Politics

    • Political science is the systematic study of governments, of the methods by which governments seek to control people, and of the techniques through which people try to influence government.
    • Chapter 3, "Developing Conceptual Acuity", illustrates some ways in which we can systematically increase our ability to think systematically about politics.

  • The Problems with Polls

    • In practice, pollsters need to balance the cost of a large sample with the reduction in sampling error.
    • A sample size of around 500 – 1,000 is a typical compromise for political polls .
    • Since some people do not answer calls from strangers or refuse to answer the poll, poll samples may not be representative samples from a population due to a non-response bias.
    • Error due to bias does not become smaller with larger sample sizes--taking a larger sample size simply repeats the same mistake on a larger scale.
    • In statistics, self-selection bias arises in any situation in which individuals select themselves into a group, causing a biased sample with non-probability sampling.

  • Analyzing Data

    • It expresses the amount of random sampling error in a survey's results.
    • The confidence level, the sample design for a survey, and in particular its sample size, determines the magnitude of the margin of error.
    • A larger sample size produces a smaller margin of error, all else remaining equal.
    • If the exact confidence intervals are used the margin of error takes into account both sampling error and non-sampling error.
    • Polls typically involve taking a sample from a certain population.

  • Telephone and Internet Polling

    • The difference between probability samples (where the inclusion probabilities for all units of the target population is known in advance) and non-probability samples (which often require less time and effort but generally do not support statistical inference) is crucial.
    • Probability samples are highly affected by problems of non-coverage (not all members of the general population have Internet access) and frame problems (online survey invitations are most conveniently distributed using e-mail, but there are no e-mail directories of the general population that might be used as a sampling frame).
    • Due to the lack of sampling frames, many online survey invitations are published in the form of an URL link on web sites or in other media, which leads to sample selection bias that is out of research control and to non-probability samples.
    • Traditional solicitation modes, such as telephone or mail invitations to web surveys, can help overcoming probability sampling issues in online surveys.
    • Telephone polling is also fairly cost efficient, depending on local call charge structure, which makes it good for large national (or international) sampling frames .

  • Bureaucratic Reform

    • In 1801, President Thomas Jefferson, alarmed that Federalists dominated the civil service and the army, identified the party affiliation of office holders, and systematically appointed Republicans.
    • President Andrew Jackson in 1829 began the systematic rotation of office holders after four years, replacing them with his own partisans.
    • By the 1830s, the "spoils system" referred to the systematic replacement of office holders every time the government changed party hands.

  • Conducting Polls

    • Steps to conduct a poll effectively including identifying a sample, evaluating poll questions, and selecting a question and response mode.
    • Contact sampled individuals and collect data from those who are difficult to reach
    • Survey samples can be broadly divided into two types: probability samples and non-probability samples.
    • Stratified sampling is a method of probability sampling such that sub-populations within an overall population are identified and included in the sample.
    • If the response option is yes/no then you will only know how many, or what percent, of your sample answered yes/no.

  • Constructing Public Opinion Surveys

    • An opinion poll is a survey of public opinion from a particular sample, and is designed to represent the opinions of a population.
    • An opinion poll, sometimes simply referred to as a "poll," is a survey of public opinion from a particular sample .
    • Useful in describing the characteristics of a large population assuming the sampling is valid.
    • Self-selection bias: Although the individuals chosen to participate in surveys are often randomly sampled, errors due to non-responses may exist.
    • Advance letter: A short letter sent in advance to inform the sampled respondents about the upcoming survey.

  • The Importance of Accuracy

    • One reason for their previous successes was the use of a very large sample population.
    • In 1936, the Digest conducted their presidential poll with 2.3 million voters, a huge sample size.
    • However, the sample turned out to be an inaccurate representation of the general population as those polled were generally more affluent Americans who tended to have Republican sympathies.
    • At the same time, George Gallup conducted a far smaller, but more scientifically based survey, in which he polled a more demographically representative sample.
    • Additionally, good research will "look for differences that make a difference" and "build in reality checks. " Researchers are also advised to replicate their polls, that is, "to see if identical analyses yield similar results for different samples of people. " The next two rules urge researchers to "compare like with like" and to "study change;" these two rules are especially important when researchers want to estimate the effect of one variable on another.