Examples of Stratified Sampling in the following topics:


 Steps to conduct a poll effectively including identifying a sample, evaluating poll questions, and selecting a question and response mode.
 Survey samples can be broadly divided into two types: probability samples and nonprobability samples.
 Stratified sampling is a method of probability sampling such that subpopulations 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.

 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 nonresponse bias.
 Error due to bias does not become smaller with larger sample sizestaking a larger sample size simply repeats the same mistake on a larger scale.
 In statistics, selfselection bias arises in any situation in which individuals select themselves into a group, causing a biased sample with nonprobability sampling.

 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 nonsampling error.
 The margin of error for a particular sampling method is essentially the same regardless of whether the population of interest is the size of a school, city, state, or country, as long as the sampling fraction is less than 5%.

 The difference between probability samples (where the inclusion probabilities for all units of the target population is known in advance) and nonprobability 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 noncoverage (not all members of the general population have Internet access) and frame problems (online survey invitations are most conveniently distributed using email, but there are no email 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 nonprobability 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 .

 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 .

 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.
 " Researchers are also advised to replicate their polls, that is, "to see if identical analyses yield similar results for different samples of people.

 In 1936, its 2.3 million "voters" constituted a huge sample; however, they 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 demographically representative sample.


 Public opinion can be accurately obtained through a random sample survey, if done correctly.