Jajal pamanggih

Jajal pamanggih mangrupa surveys pamanggih maké sampling. Hal ieu dijieun keur ngagambarkeun pamanggih tina populasi ku méré patarosan ka sajumlah leutik anggota populasi sarta nga-ekstrapolasi jawaban kana grup nu leuwih gedé.

Potensi keakuratan

Margin kasalahan

Sakabéh jajal mibanda margin kasalahan, nu mangrupa fungsi tina jumlah anggota nu ngajajal.  Margin kasalahan ngagambarkeun kamungkinan kasalahan dina prosés sampling, tapi  teu ngagambarkeun sumber kasalahan, saperti ukuran kasalahan atawa kasalahan dina prosés data.  Jajal nu mibanda sampel 500 anggota mibanda margi kasalahan 4.5% keur estimasi persentese tina sakabéh populasi. Margin kasalahan 4.5% hartina yén 95% tina waktu prosedur nu dipaké bakal méré estimasi dina 4.5% persentase nu keur di-estimasi.

Saprak anggota nu milu dina jajal nolak, sampel jajal teu ngagambarkeun sampel dina populasi, sarta karakter matematikna ditandaan ku béda tina populasi. Margin kasalahan béda jeung persentase estimasi, sarta persentase estimasi tanda béda tina populasi, margin kasalahan dina hasil jajal teu ngagambarkeun populasi nu sabenerna.

Kalimah patarosan

Milih kalimah sarta urutan patarosan dina jajal pamanggih kacida perlu, ieu bisa mangaruhan kana hasil jajal pamanggih.  Thus comparisons between polls often boil down to the wording of the question.
One way in which pollsters attempt to minimize this effect is to ask the same set of questions over time, in order to track changes in opinion. The most effective controls, used by attitude reséarchers, are:

 asking enough questions to allow all aspects of an issue to be covered and to control effects due to the form of the question (such as positive or negative wording), the adequacy of the number being established quantitatively with psychometric méasures such as reliability coefficients, and
 analyzing the results with psychometric techniques which synthesize the answers into a few reliable scores and detect ineffective questions.

These controls are not widely used in the polling industry...

Nonrepresentative samples

Another source of error is the deliberate or accidental use of nonrepresentative samples. For example, when home telephones were rare, telephone sampling had a built-in error because most of those surveyed were well-to-do.

Péople asked to participate in opinion polls also have the right to refuse; this méans that the sample is self-selected and consequently a non-probability sample. The validity of the results and of the statistical techniques used to derive characteristics of the sample such as the margin of error are therefore highly questionable.

Polling organizations

There are many polling organizations.  The most famous is the Gallup poll, créated by George Gallup.

Other major polling organizations in the United States include:
Quinnipiac Polls, run by the University of Connecticut, and started as a student project.
The Pew Charitable Trusts conducts polls concentrating on media and political beliefs.
The Harris Poll
Nielsen Ratings, virtually always for television.

All the major television networks, alone or in conjunction with the largest newspapers or magazines, in virtually every country with elections, operate polling operations, alone or in groups.

The best-known failure of opinion polling to date in the United States was the prediction that Thomas Dewey would deféat Harry S. Truman in the 1948 Presidential election.  Major polling organizations, including Gallup and the Roper Center, indicated a landslide victory for Dewey.

Tempo oge
 Exit poll
 interval kapercayaan
 push poll
 All-Russia Center for the Study of Public Opinion

Psikométrika